How to fix a u-lock that has been rusted shut around handle bars for several years?

cross-posted from: https://sh.itjust.works/post/64521441

Things that have not worked (so far):

Youtube video recommended a specific bike lubricant but that didn't work.

I read hitting it with a hammer could help knock some of the rust loose but so far nada.

How it got stuck: I got doored pretty bad a few months before getting pregnant several years ago and basically stopped riding completely afterwards bc drivers are such assholes in the city where I live.

My stbx always chastised me for storing it in the house, and after we moved together the last time in 2021, he started making me keep it outside under a tarp.

Now he's gone and it's my only means of transportation, but the lock is stuck like a yoke around the neck.

I can feel something turning inside after a half revolution when I try to unlock it with the key, but I can't even remember if it's supposed to make a full revolution and is getting stuck halfway or if that's as far as it's supposed to turn (as in, is the rust is inside the barrel or the keyhole?).

Any other tips or ideas to get it open?

My dad said he thinks worst case scenario we can just cut it off, but it's a kryptonite lock and I thought they were supposed to be impossible to cut?