GPS pass through to waydroid is possible by modifying images but will need high spec phones (works well in pinetab2 or flx1 but not in pinephone or Librem 5).

I use Pure Maps often and it works well. Offline is a must, battery won't survive if you have to keep a network connection open. GNOME would be best long run, maybe. Organic Maps has a lot of active development on Android and iOS, it would be excellent if that could be leveraged on mobile Linux. I do not have experience w/ osmin or mepo. I dislike having to keep Waydroid around.

Keeping GPS pass through last because it's either already working (FLX1) or inconvenient for other reasons (Librem 5 and PinePhone have too low RAM to run Waydroid properly).

Since our environment is GNOME based I'm preferring the GTK option, which will blend in the best. Organic Maps and Pure Maps both use QT and need UI improvements. Pure Maps may need less work to start, but with Organic Maps, in the long run, adding features will pay off by adding them to multiple platforms.

Definitely use something that makes use of vector tiles and real-time rendered maps. Anything else is just not good from a UX perspective.

Hacking something together with MapLibre Native may also be a good option. We have support for GLFW but you can also use Qt on Linux. You need to use a tile provider or host your own tiles.