I wouldn't straight out recommend fly.io. See, part of Heroku's value proposition was their excellent support. I had asked fly.io to delete my account since there wasn't a provision to delete it from their interface and they never bothered to reply and put me in some kind of shadow ban from re-registering with my email.

I mean if this is how you're going to treat your customers, then good luck! I'm yet to try out railway.app and..looks interesting to say the least.