Heroes of Might and Magic II
is on Gameboy color (and more, but only GBC seems to be an option for Switch, unless DOS box works fine too?).
it's probably easy to find a GBC emulator with retroarch or lakka.
I don't know if GBA emulators can run GBC too. (maybe mGBA or VBA next?)
Heroes of Might & Magic III
is apparently on Android, Linux, Dreamcast (and more but these 3 are working on Switch)
is a Dreamcast emulator homebrew (nro), so you can use atmosphere or your preferred cfw.
Android is now possible very easily with LineageOS
, and a dedicated SD card. you boot your switch into a Nvidia Shield.
Actually, while in Android, you probably will find lot of GBC emulators on google appstore to play Heroes of M&M II
There's also L4T linux for Switch (another dedicated SD card), if you want to play the linux version of the game, but you might need to know how linux work, and how to install the game.