What cloud platform should a Python developer learn?

You should learn core concepts that compose the cloud platform. Things like docker containers, databases, object storage, load balancers, NAT/Networking/DNS, e.t.c.

Cloud platform specific stuff is way easier to learn compared to the core concepts.

I’d start with terraform against a cloud of your choice.

Personally I’ve been using oracle as a test bed for that given their generous free tier but for production I’d probably use GCP

You should learn cloud platforms, not a cloud platform.

Also avoid to waste your life learning proprietary technology that will become obsolete and discontinued. Software containers are likely there to stay, the latest serverless framework from a cloud provider will likely not.

What about fly.io? Since Heroku discontinued its Free tier, lots of people praise it for its simplicity.

As a person, who played quite a bit with Digital Ocean and would have loved to skip the server setuping, I think it would be perfect for my future projects as well.

Heroku has been useful to learners so they don't have to deal with the complexity all at once. Render is a good alternative offering a similar experience.

Start with Docker and a PaaS like Heroku/Render/Fly/Dokku to get the core web service things without getting lost in all the proprietary vendor-specific things, or the madness of building one's own cloud just to run some web applications (Kubernetes etc).

I’ve heard good things about GCP, but I would think AWS open more doors since it’s more popular.

Personally I stay away from Azure, IMHO it just seems clunky. (Just my personal opinion so take it with a grain of salt.)

BTW, if you’re new to cloud stuff this resource might come handy: https://cloudresumechallenge.dev/

Best of luck!

Learning Kubernetes abstractions: which problems are they supposed to solve and how exactly they do it (trade offs) may be useful whatever cloud platform you choose later (in automation/scripting space).

What provider(s) do your customer(s) or employer(s) use?

Start there

Can the cloud help you with a specific goal?