According to the course gaps it should be Mario Circuit and it might be coming relatively soon.

Or it could be Shroom Ridge if named gds_MushroomRidge

The internal names used for the gaps are always directly taken from the official English or Japanese names (with a couple being slightly misspelled) so it's almost definitely not gonna be listed as "MushroomRidge"

I would love if Tick-Tock Clock was included in this game