For Bootstrap 5 have a look at Vartheme (Bootstrap 5 - SASS)
A base theme for Varbase standard websites.
Based on the Bootstrap Barrio theme (Bootstrap 4 - SASS).
Varbase documentation
Check out Varbase documentation for more details.
Vartheme BS4 home page after a fresh install of Varbase
Use With Varbase Distribution:
This theme is best used with Varbase distribution.
Can be installed with any Drupal 9 site. Even if installed with the Minimal or Standard profile.
However, using it with Varbase gives you way much more cool stuff!
Varbase documentation
Check out Varbase documentation for more details.