Early iOs and Android icons were one of the last offshoot of the style called "Frutiger Aero"
Flat icons don't necessarily bad and undetailed, it's just harder to create something more recogniseable with less tools, but I actually like the order, that they look like they are related to each other. Back in the day I created icon packs for the programs I used on pc, so my desktop would look clean and uniform.
Design styles are in a cycle, just wait some years and they will show up again, I'm sure. There is already some connection with the new style of windows 11.
Because they have different appid. Izzy version is
app.organicmaps.web
fdroid version isapp.organicmaps
(you can see this in the url). Google version uses the same appid as fdroid. You can't have two apps installed with the same appid, but this way you can have both installed at the same time.I guess organic devs wanted separate appid for their 2 versions and fdroid just went with the default, original one.
So the 3 versions: