Even though it looks like a great product initially, it has a lot or errors and bugs when you are trying to actually build something more robust than a toy app.
Local development is a massive pain with random bugs.
The response time of the database also varies all over the place.
But the most important problem that we faced, was having so much of application logic in the database.
Row level security is their "foundational piece", but there is a reason why we moved away from database functions and application logic in database over a decade ago: that stuff in unmaintainable.
There is also really poor support and at the end of the day, the whole platform felt like a hack.
I think now, for most apps with up to 500_000 users (with 10_000 concurrent realtime connections) PocketBase is the best PaaS out there having tested a bunch of them.
A single deployable binary which PocketBase provides is a breath of fresh air.
Anything more than that, just directly being on top of bare metal or AWS / GCP is much better.