The Heroku style of PaaS just isn't very interesting to most large businesses that actually pay for things. The world basically moved on to Kubernetes-based products (see Google and Red Hat)--or just shutdown like a lot of Cloud Foundry-based products. Yes, many individuals and smaller shops care more about simplicity but they're generally not willing/able to pay a lot (if anything).

I find render.com basically as good as Heroku and certainly much better than fly.io's unpredictable pricing

Heroku and Ruby, for me, was the 21st century answer to 'deploying' a PHP site over FTP.

The fact that it required nothing but 'git push heroku master' at the time was incredible, especially for how easy it was to spin up pre-prod environments with it, and how wiring up a database was also trivial.

Every time I come across an infrastructure that is bloated out with k8s, helm charts, and a complex web of cloud resources, all for a service not even running at scale, I look back to the simplicity we used to have.

I completely agree that there's nothing comparable to old-school Heroku, which is crazy. That said, Cloudflare seems promising for some types of projects and I use them for a few things. Anyone using them as a one-stop-shop?

For me Northflank have filled this spot. Though by the time I switched I was already using Docker so can't speak directly to their Heroku Buildpack support.

vercel goes a step further, and (when configured this way) allocates a new hostname (eg feature-branch-add-thingg.app.vercel.example.com) for new branches, to make testing even easier.