Documentation changes ... Breaking Dropped .btn-block for utilities. Instead of using .btn-block on the .btn , wrap your buttons with .d-grid and a .gap-* utility ... Sass · Grid updates · Content, Reboot, etc · Components
Renamed the .hidden-print utilities to use the display utility naming scheme. More info under the Responsive utilities section of this page. Added .float-{ ...
Use Bootstrap's utility API to modify any of our included utilities or create your own custom utilities for any project. Import Bootstrap first, then use Sass ... Bootstrap Expo · Get started with Bootstrap · Bootstrap 3.4 · Bootstrap
I've created a Bootstrap 5 Migrate Tool script which scans all pages/templates in a folder and replaces all the Bootstrap 4 classes with Bootstrap 5 classes.
The short answer is NO. You cannot automatically upgrade from Bootstrap v4 to v5. Bootstrap does not provide migration tools like Angular does, for example.