Technically aren't most android apps limited to ARM?

There's certainly some, but I don't think most.

I'd guess most apps are bytecode only, which will run on any platform. Some apps with native code have bytecode fallbacks. Many apps with native code include multiple support for multiple architectures; the app developer will pick what they think is relevant for their users, but mips and x86 are options. There were production x86 androids for a few years, some of those might still be in user bases; mips got taken out of the Native Development Kit in 2018 so probably not very relevant anymore.