[ihuman]

The GBA (original and SP) also supported OG Gameboy games, but the Gameboy Micro only supported GBA games

The 3DS also had games from other consoles for sale in the eShop, but they were emulated (GB, GBC, Game Gear, NES, SNES). If you bought a 3DS before the price drop, you could also play some GBA games. These are also running natively, not emulation https://en-americas-support.nintendo.com/app/answers/detail/...

[Dwedit]

Game Boy Micro can still enter GBC mode, it just can't read any cartridges. It's missing the switch which is normally triggered by the cartridge shape, and also missing the voltage conversion circuitry.