Rainbow Road SNES has appeared in 4(Deluxe and Tour don’t count, deluxe as its 8 with the original DLC and I personally don’t count tour because it’s on mobile and most of the steering and driving is done for you) out of 8 games, half the roster.
These games are as follows:
SNES in Special Cup
GBA Mario Kart Super Circuit in Extra Cup (not available through normal unlockable means we see today)
Mario Kart 7 in Lightning Cup
Mario Kart 8 as DLC Super Bell Cup (and Deluxe as Super Bell Cup)
To say in the track would appear in “almost every Mario Kart game” is a bit of a hyperbole, but it is in a lot if them. Whether the track is s masterpiece is however up for debate. I personally prefer the three iterations of Mario Kart 64’s rainbow road.
Caption this Meme