Difference between Bootstrap 4 and Bootstrap 5 

Here is the list;

BASIS OFBOOTSTRAP 4BOOTSTRAP 5
Grid SystemIt has 5 tier (xs, sm, md, lg, xl).It has 6 tier (xs, sm, md, lg, xl, xxl).
ColorIt has limited colors.Extra colors added with the looks, A card improved color palette. there are various shades available to choose.
JqueryIt has jquery and all related plugins.Jquery is removed and switched to vanilla JS with some working plugins
Internet ExplorerBootstrap 4 supports both IE 10 and 11.Bootstrap 5 doesn’t support IE 10 and 11.
Form elementsRadio buttons, checkboxes have different look in different OS and browsers. The form uses whatever default browsers provide.The look of form elements will not change, on different OS or browser. The forms can be customized and form controls can be added, they would not depend on browser. 
Utilities APIWe cannot modify utilities in bootstrap 4Bootstrap 5 gave freedom to modify and also create our own utility
GutterWe use .glutter with fontsize in pxWe use .g* with fontsize in rem
Vertical ClassesColumns can be positioned relativeColumns cannot be positioned relative
Bootstrap IconsBootstrap 4 doesn’t have its own SVG icons, we have to use font-awesome for icons.Bootstrap 5 have its own SVG icons
JumbotronIt supports.It doesn’t support jumbotron.
Card deckThe card deck is used to create a set of cards with equal width and height.Card deck class in removed in bootstrap
NavbarWe have inline-block property and we will get white dropdown as default for dropdown-menu-dark class.Inline-block property is removed and we will get black dropdown as default for dropdown-menu-dark class.
Static Site GeneratorBootstrap 4 uses Jekyll software.Bootstrap 5 uses Hugo software as it is fast static site generator.
flexbox gridthis makes easier to implement vertical designs, and the columns and rows can easily be implemented. the classes justify-center-content can directly be used to align according to the requirement.advanced grid system is made available , also columns don’t have relative positions.  
RTL SupportIt does not enable RTL(Right to Left) switching.It enables RTL(Right to Left) switching.
Offcanvas ComponentIt does not support Offcanvas Component.It supports Offcanvas Component(that is it is available now).

Reference

https://jekyllrb.com/

https://gohugo.io/

Bootstrap Multiselect

Bootstrap Multiselect is a JQuery based plugin to provide an intuitive user interface for using select inputs with the multiple attribute present. Instead of a select a bootstrap button will be shown w dropdown menu containing the single options as checkboxes.

Read more by clicking on below link;

https://davidstutz.github.io/bootstrap-multiselect/

Here is the Git repo for download

Create your own web font with just the icons you need

I love Bootstrap Icons. It has a large selection of quality icons and it’s open source so can be used for free (subject to license terms and conditions).

The simple way to use the icons on your website is to use the web font, but that means you are including all 1,800 plus icons (as of v1.10), albeit the file is a reasonable 120kb.

But using a free online tool, you can create your own web font with just the icons you need.

Here’s how I use Bootstrap Icons…

Download the icons

Go to the Bootstrap Icons download page on Github and download the bootstrap-icons-x.zip ZIP file.

Choose which icons you want to include

Unzip and open the file. The icons are the SVG files in the root of the ZIP file.

You may find it easier to create a temporary new folder to store the icons you want in.

Make your own web font

I use the IcoMoon app to easily create a custom web font.

Head on over to icomoon.io/app.

Press Import Icons (near top left of page) and select all of the icon SVG files that you want in your font.

You can either add files one at a time or you can select multiple files at once.

Once you proceed, your selected icons will appear as “Untitled Set”. You still need to highlight each of your icons to select them so that they get included in your custom web font. You can select one at a time or multiple select or select all.

Next step is to press Generate Font (bottom right of page). This will show details of your new font and expose a Download button so you can download a ZIP file containing what you need.

The ZIP file has style.css which you will need to include or better still, add to your HTML template or existing style sheet.

There is also a fonts folder which you will need to copy to your website as it contains the actual web font.

Lastly, there is demo.html which contains examples of how to include your chosen icons in your HTML.

The icon classes are named icon- and then the file name without extension. So you would typically use as follows:

 <span class="icon-check2"></span>

To use these fonts in ASP.NET Core, Add them to wwwroot -> lib folder (create a new folder). Open _Layout.cshtml view in Shared folder and add this line in header;

<!--Bootstrap icons-->
<link href="~/lib/bootstrap-icon/style.css" rel="stylesheet" />

You are ready to use these icons.

Accessibility

If your icon is purely decorative, then hide it from screen readers:

<span class="icon-arrow-right-circle" aria-hidden="true"></span>

If your icon is semantic, then you will need to provide alternative text for screen readers. This example is based on what font awesome recommends:

<span aria-hidden="true" class="icon-bluetooth" title="Bluetooth"></span>
<span class="sr-only">Bluetooth</span>
<span>enabled</span>

Credits:

http://johna.compoutpost.com/blog/1275/how-i-use-the-new-bootstrap-icons-web-font/

How to use the new Bootstrap Icons v1.10 web font

With the release of Bootstrap Icons v1.10, there is now an easy-to-use web font. Here’s how you can use the new web font in your web pages.

Step 1 – Download the Bootstrap Icons files

Go to icons.getbootstrap.com and download the latest release. There is a download button at the top-right corner of the page.

Step 2 – Install the Bootstrap Icons files

To use the web font on your web site you will need to extract a few files from the ZIP file.

From the fonts folder you will need bootstrap-icons.css and the fonts folder (the one inside the first fonts folder) with the bootstrap-icons.woff and bootstrap-icons.woff2 files.

Copy the CSS file and fonts folder to your website. You can copy the files to your web root folder but typically you would copy them to a folder that contains your other CSS files.

Step 3 – Include the Bootstrap Icons CSS file in your web pages

To be able to use the fonts in your web pages you will need to include the bootstrap-icons CSS file in your HEAD section of your HTML. How this is done will vary on the type of website. If you have simple HTML pages then you would need to add this to each page where you want to use the web font. If you are using a content management system like WordPress then this can be done in a template. If you are not sure use Google to search for how to add a CSS file to your CMS.

To include the CSS file you would add something like this:

<link href="bootstrap-icons.css" rel="stylesheet">

(CSS file is in same folder as the HTML document)

<link href="/bootstrap-icons.css" rel="stylesheet">

(CSS file is in your web root folder)

<link href="/css/bootstrap-icons.css" rel="stylesheet">

(CSS file is in your CSS folder)

Step 4 – Using the Bootstrap Icons web font

To include one of the icons you simply add the web font code that you can find on the Bootstrap Icons website.

For example:

<i class="bi-alarm"></i>

Each icon has it’s own class (eg. bi-alarm), and you can find these by clicking an icon on the Bootstrap Icons website.

Full example:

<!doctype html>
<html lang="en">
<head>
	<meta charset="utf-8">
	<meta name="viewport" content="width=device-width, initial-scale=1">
	<link href="https://cdn.jsdelivr.net/npm/bootstrap@5.0.0-beta1/dist/css/bootstrap.min.css" rel="stylesheet" integrity="sha384-giJF6kkoqNQ00vy+HMDP7azOuL0xtbfIcaT9wjKHr8RbDVddVHyTfAAsrekwKmP1" crossorigin="anonymous">
	<link href="bootstrap-icons.css" rel="stylesheet">
	<title>Hello, world!</title>
</head>
<body>
	<div class="container">
		<h1>Bootstrap Icons v1.2 Example</h1>
		<p>
			<i class="bi-alarm"></i>
		</p>
	</div>
	<script src="https://cdn.jsdelivr.net/npm/bootstrap@5.0.0-beta1/dist/js/bootstrap.bundle.min.js" integrity="sha384-ygbV9kiqUc6oa4msXn9868pTtWMgiQaeYH7/t7LECLbyPA2x65Kgf80OJFdroafW" crossorigin="anonymous"></script>
</body>
</html>