My personal goto-solution for those requirements -- well 1 cloud provider, I'll follow up on that in a second -- would be using ECS or an equivalent service. I see the OP was a critic of Docker as well, but for me, ECS hits a sweet spot. I know the compute is at a premium, but at least in my use-cases, it's so far been a sensible trade.

About the 2 cloud providers bit. Is that a common thing? I get wanting migrate away from one for another, but having a need for running on more than 1 cloud simultaneously just seems alien to me.

Last time I checked ECS was even more expensive than using Lambda but without the ability of fast starting your container, so I really don't get the niche it fits into, compared to Lambda on one side and self-hosting docker on minimal EC2 instances on the other side.

Actually, I totally agree. ECS (in combination with secret manager) is basically fulfilling all needs, except being not so easy to reproduce/simulate locally and of course with the vendor lock-in.