Interval training is a pretty solid choice in general, which includes the Tabata methods. Try Tabata front squats some time.
I’ve done Tabata squats with 95 pounds once… never again. I had trouble walking down stairs the entire day after doing that.
Dude, Mondays are my leg days, and by Wednesday I can barely get out of or into a chair. This morning I had to soak in the tub to feel loose enough to stand for a shower. It’s a price that’s paid by lots of people every week.
If you want to build muscle, then you’re going to suffer. Guaranteed.
Right now I feel that your issues are all upstairs and you need some re-programming. Once you read the beginner stuff and really identify what your goals are it’s going to fall in place. I’m impressed by your willingness to learn so far though.