There's a ton, sharing in case you've never seen them.

In a linear graph from "Heroku" to "VPS do-it-yourself":

     |------------------------------------------------------------|
    Heroku    Render     Railway     NorthFlank    Fly      DigitalOcean

That's how I would place them from easiest to hardest. Of course DigitalOcean is not a PaaS but bear with me.

I use Render for https://www.gamedrop.gg/ and it works really well for me, very hands off.

We did a bake off 18 months ago and identified ~5 similar platforms at the time. Fly.io and Render were 2 of them.

We chose Render and have been happy with things just chugging along as they were on Heroku.

Their runtime seems to take up quite a bit more RAM, but the IAC is a great addition resulting in 100% consistent environments.

I am not surprised. There are a handful of competitors but I believe the ship has sailed. I am a complete AWS dunce but it's too easy for me to spin up an ECS with spot machines and run my python app on it. When Heroku hit the scene and for many years, there was no easy alternative. You had to go and provision your own machines to then setup.

The best alternative I found is render.com

It has this feeling of "just works", and documentation is pretty good.

Fly.io maybe?

I just use Dokku on a VPS and it works fine.

Sure it might not scale but Heroku didn't either.