> why should I not be able to do so on my phone?
Strictly speaking, you can. Enable developer mode, connect your phone to your Mac (you need a Mac), and you can build and install whatever code you want.
Asterisks being that your phone will uninstall it after a while I think, and you need to create a free account for Xcode.
You actually need a paid account, even for local installs, if you use certain tech, like NFC
Seriously? I have a custom Android app that I use. It's mostly vibe coded now, which I'm a bit embarrassed about, but demonstrates that the bar for custom software is very low at the moment and getting lower.
I considered getting an iPhone to replace my S-series Samsung, the only reason I stayed with Samsung is for the S-Pen. Had I gone with iPhone I would not be able to write and run my own software? That's absolutely ridiculous.
Strictly speaking, I can't, I don't own any Mac nor planning to do so
The up to 3 apps per device stay but cannot be opened after 7 days until refreshed.
And "whatever code you want" here excludes JIT compilation, or as I understand it memory that is both writable and executable, as your app would require a special 'entitlement' from Apple.