Does such a device exist? I only want to emulate DMG/GBC games, looking for something cheap, vertical and with only two buttons.

Can be a Gameboy clone or an emulator based handheld. Honestly emulation would be better, I'd like to use (shaders) a monochrome screen for DMG games and color screen for GBC games.

I have no interest in emulating other systems, got a Steam Deck for those. I just prefer the form factor of Gameboys so that's why I'm interested in such a device.

Found so many Anbernic and other similar handhelds but they are overkill. I don't even need 4 buttons, just 2 buttons will do.

ROM support and rechargable battery is a must. I'm staying away from real hardware because there is a chance they might stop working after so many years of usage, flashcards are expensive and they lack rechargable batteries.