Lots of newer cars have 3/4g modems that report mileage. For my car, the dealer can access a bunch of info remotely such as oil life, mileage, etc.
Like already said, On newer cars it’s harder to rollback the odo as multiple modules in the car will record mileage. So they have to make sure every module like the ecm, bcm, etc. is overwritten with the correct mileage.
So yeah it’s possible but harder if you know some shady people
I think it’s common for people going over their kilometres on their lease agreements to rollback mileage. Just to avoid extra costs. I don’t think any reputable dealer would do that and risk getting caught