I actually started my startup with this approach -- good old Django.

Lasted for a year until we had users wanting to do complex interactions on the frontend.

Simple CRUD apps are fine, but users expect a lot of interactivity these days where things on the screen interact with each other.

The nice thing about Django, though, is that you can easily switch to api-based backend with DRF or Django-Ninja. We used DRF but if I were to do it again, I'd choose ninja.