My main computing device is a Lenovo x220 with xubuntu. It does 99% of what I need; I love it.
I also own a 2021 Ipad Pro. I bought it as a Nomad Sculpt and Procreate machine. However, I've really been getting into graphics programming lately and would love to start building my own custom tools and augmented reality graphics sketches. I'm specifically interested in getting some experience in with the Metal API.
Unfortunately, I don't have $2k or even $500 to drop on an apple compute device. I have an old, very beat up 2010 MBP, but I don't know how much use it would be. I certainly wouldn't want to develop on it.
Are there any reasonably priced services that I could use to compile apps for IpadOS? It seems like in this day and age I ought to be able to write the whole thing on my preferred xubuntu machine, then send that over to something else for "apple-compliant-compilation" and so on and so forth.
just install Swift Playgrounds and see first if that is something you actually feel like doing.
https://deurell.github.io/posts/playground-shaders/
https://twitter.com/AndyQ/status/1471553504418410497
While not fully features and comes with caveats, it is already a stepping stone to experiment.
Others will tell you to learn Vulkan and use MoltenVK for the iPad.
Now, I would rather advise to pick a middleware like Ogre 3D, Unity, Unreal, specially if you are getting into the field.
Then you can consider if it is worthwhile the monetary investment to carry on.