Think Digital Ocean, except even faster (no login), and they are ephemeral (destroyed after 60 minutes or so if you don't upgrade it to paid).
When I was at Microsoft we prototyped this idea (called it "Azure Instant"), but years later still looks like it hasn't seen the light of day.
Someone must have made this by now, right?
1: https://jvns.ca/blog/2021/01/23/firecracker--start-a-vm-in-l...