I would stay away from any startup for production workload.

Made the mistake. Never again.

Fly, railway, render. Avoid. All have weird show stopper bugs for any reasonable scale and you will fight against the platform compared to using big cloud.

And big cloud works better even in cases where PAAS is advertised as simpler (google cloud run and build is as easy to setup as railway but you have much more knobs to control traffic, routing, roll out etc)