Just out of curiosity, here is top level comparison; first one is managed instance, second one is Single database;
Top level comparison;
Databases level comparison;
System level databases;
Single database has just master database;
master database object layout
System level security
Single database does not have these root level objects;
Server Objects, Replication, Management, SQL Server Agent, XEvent Profiler
Integration Services Catalogs doesn’t exists on both services. Azure Data Factory integration services need to be provisioned to create SSIS database under Integration Services Catalogs.
Reporting services does not exists here. Power BI integrated Reporting services needs to be provisioned.