Nintendo just announced this on there twitter account.
Buckle up, because #MarioKartTour will be available on 9/25. Follow @mariokarttourEN for more information heading into the game's release. pic.twitter.com/1V0njTVWRx
— Nintendo of America (@NintendoAmerica) August 27, 2019
Game was in beta a few months ago with some retro tracks. I believe impressions were pretty mixed back then.
Check out my lastest games review: Fast RMX and Snipperclips: Cut it out Together