You pretty much have two options for legit tailgating (pour one out for the old days of the river flats):
1) go on StubHub etc. (or you can look/post in the For Sale board here on GopherHole) and buy a parking pass to one of the main lots by the stadium. (See map here:
https://pts.umn.edu/sites/pts.umn.edu/files/2021-09/CampusOverviewMap.pdf ) This will be expensive, but if you're just coming for the one game then this is the most fun experience.
EDIT: 1B) there is tailgating on at least one West Bank lot. This experience would be somewhat inbetween 1 and 2, though I think you'd have a fair bit of walk with no shuttle bus. And you'd still have to buy the pass.
2) the easy button is the State Fairgrounds lot (S108 - map here:
https://pts.umn.edu/sites/pts.umn.edu/files/2021-08/108.pdf ) This is $10 per vehicle and includes free shuttle busses to and from the stadium. The busses run all the time with tons of them right before and right after the game. You won't have any problem. You can even tailgate well into the game and show up late, they still have periodic busses (done that a fair share of times!)
But, it is isolated as its own thing. Of course, you can take a bus early and wander around the lots close to the stadium, as you please.