In my experience flask is great until it isn't - I've seen quite a few projects which outgrew it, and the lack of django's batteries and guard rails left a maintenance nightmare. Not sure if it'll be helpful, but as a result I wrote nanodjango, which lets you write a django site in a single file, then convert it to a full project if you outgrow it.
Nanodjango 0.8 is out, adding async view and ASGI support. Now you can write async single file scripts that look like Flask or FastAPI, but with all #django features like models, auth, admin etc.