In what world would you expect it to NOT be compatible with Switch cartridges?
- Game Boy, Color, Advance - backwards compatible
- GameCube, Wii - backwards compatible
- Wii - Wii U - backwards compatible
- DS - DSi - 3DS - N3DS - backwards compatible
For all their faults, Nintendo have been strong with backwards compatibility for 30+ years, the only exceptions being the SNES (NES backwards compatibility existed initially but was dropped), N64 (fucking complex custom architecture and final cart based console) and Virtual Boy (lol)
This is 7 years now since the launch of the switch. That's longer than the period between the NES western launch to the SNES 1985-1991, longer than SNES to the N64 (1991-1996), longer than the N64 to the GameCube (1996 - 2001), longer than GameCube to the Wii (2001 - 2006), Wii to Wii U ( 2006 to 2012) and Wii U to Switch (2012 - 2017)
The ONLY exception being the OG Gameboy to GBC, 9 years.
Me, with a mate a week ago on Resident Evil 5.