Plenty of useful apps that cannot run on iOS. Mostly Termux and SDR-related apps (rtl_tcp server, SDR++, SatDump, Welle.io, SDRAngel, Dump1090,...)

I can run full-on desktop in Termux and access it via VNC server. I can also access it via SSH server. I can run a web server, HTTP proxy server, Kiwix server, Navidrome server, Jellyfin server, port-forward using socat. And that's just what I use or tried. In the past there was someone on Reddit running a public BBS server on an Android phone in Termux.

There's likely many other apps I use not available on iOS.

So if I'll be switching to a different platform, maybe PinePhone running Arch Linux with Plasma mobile? Probably only as a secondary phone for now though.

iPhones are too close to feature phones for me. Best thing they can run is probably a browser.