I’m having a good time even on an 11th gen mobile Intel processor with its iGPU. For more demanding games I use FSR to get much more bang for buck from the iGPU, on Linux it’s pretty easy to activate in almost any game. On a side note, Waydroid (with libhoudini) also has excellent performance on this setup.

Why not install SteamOS or plain Arch Linux on the GPD devices then?

There are good things to be said about the Ally, but I find the soon-to-be-released GPD handhelds more interesting. Both are officially stated to support SteamOS (which means plain Arch and possibly other distros should also work great) and offer something different from the Deck and Ally in that the GPD Win4 is much more compact, and the GPD Max 2 has a much larger display.

LineageOS is great even without root, but I still recommend using Magisk on it for system-wide ad blocking (via e.g. AdAway) if nothing else.

A banking app may have a simple root check, or a SafetyNet check. You can use shamiko and safetynet-fix respectively to fool these, both have already been linked.