Use a week of PTO, and rent a dumpster. Take literally everything out of the garage, and place any obvious trash in the dumpster. Start methodically moving things back in, taking care to ensure each item has a "spot". Continue sifting through things and throw things away as necessary. Anything small that still works but isn't needed goes into the sell pile, anything large that could be easily fixed or still desirable goes on the curb for free pickup. You got this!
My gendernonspecificusername, you can give me all the tips in the world but if there's no drive to do something, something is very unlikely to get done.
If this garage didn't contain 250,000 small items scattered everywhere, and was instead easily identifiable trash and large easily separable items, it would have been done the first week I dedicated to it when I left my last job. Hours and hours a day, every day for slightly more than a week.
If I could keep myself on track and not get super in-depth in specific areas, I'd have the bulk organized and the small stuff contained to a smaller area I could focus on over time.
Unfortunately, we don't live in Perfect, I get easily side-tracked, and for every hour I spend cleaning, I spend another messing around with the things I find and another 20 minutes figuring out where all the pieces to that abandoned project went.
If I could pay a couple people like $100 to help for a few hours, I could probably put up all my shelving, get the big stuff taken care of, and the shelves vaguely organized into hobbies. Buuuuut I don't trust strange people I don't know and I don't want people I DO know seeing how bad it's gotten. That last part is a big problem for me.