Recently, Mario Kart Tour shut down for good. When that happened, there was no official offline version available, nor any plans for such in the future.
But it seems like fans may now have an alternative. Why? Because a fan-made revival called Mario Kart ReTour has been announced, whose release trailer can be seen here:

As you can see, it’s got everything you’d expect from a revival of the game. There are tours held on a regular basis, which are cycled through like in the original game. All the characters and karts are presented as expected. The game’s mechanics work exactly like they do in the official game. Basically, it’s a perfect continuation of the game in just about every way.
But there are a few things to note here.
First, your save data doesn’t seem to carry over. So, bad news for anyone that cared about their game progression in the original version. Due to the data being on Nintendo’s servers, it’s missing in the revival. You’ll unfortunately have to start from step 1 here.
Secondly, there was AI usage here. It wasn’t vibe coded by any means (at least 70% of the code was handwritten according to the development team), and it’s clear the team does have actual programmers onboard here…
However, if you’re against AI in all uses and feel like the presence of it kills any and all interest, then this is probably not the mod for you. The team are open about using it for some things, and that doesn’t appear to be changing any time soon.
Still, it’s at least available in some form now. So, if you’re a fan of the original version of Mario Kart Tour, check it out. It may scratch that itch after the official game’s shutdown.
Source:
Mario Kart ReTour Official Website