mGBA core via retroarch is probably your best bet for compatibility on Android.

I was really impressed with the Pokemon Coral demo a few years back. It ends after gym 4 and they are technically still working on the full game with new spriting gifs every few weeks on twitter, but seems like maybe it won't be out for another year or two, (or ever). But there are original pokemon and an original region that aims to recreate the feeling of playing pokemon GSC for the first time.

Pokemon Odyssey is what I'm playing now. New region that has a "World Tree Underground Dungeon" trope (like Dungeon Meshi) plus a bunch of islands, but there are no fakemon/originals. It has a cheat code system, support for early monotype/themed teams in the cheats, and some level of intrigue in the story that goes beyond the official games. Not everything is as it seems... Moderately challenging, and it has a level cap + an item that puts your current party one level below the cap if you want to add new members right before or right after level bosses. Pokemon learn a new move every five levels, guaranteed! (Also check the egg moves @ move relearner in the hub town guildhall, especially after you get to final evolutions.)