I use mainly flask and restful flask. However restful flask has been deprecated, so I was really interested in FastAPI. Then someone pointed out the number of open issues on the FastAPI project, so I got spooked. Flask maybe has quite a few frameworks for implementing rest API. Not sure what the future holds for Flask.
As you pointed out
> A backend comes with all sorts of baggage: databases, managing user data, authentication, backups, and increased server load.
With Flask being a microframework and barebones, going through this list becomes a chore unless you have built dozens of webapp and have some kind of template.
So I kinda gave up on web-backend entirely and moved towards firebase. Most of the complicated stuff will happen on the VPS side of things and will be communicated to firebase via the SDK.