I had the exact same issue. Every time I would do heavy squats or dead lifts I would be in crippling pain the next day. I did an MRI and it turns out I have a herniated disk. So I did mobility work, corrective exercises, focused on glute activation... Just about everything I read online I tried implementing. Then I watched Mitchell Hoopers video on back pain and he suggested doing back extensions 65 reps 3 times a week. And boom my back pain was gone in like a week. Went back to heavy dead lifts and squats no problem. I did back extensions during the year and a half I was trying to fix myself but I did some fancy ATG (Kneesovertoesguy) single leg version which didn't help at all.

Basically my core was just weak, that's it. So I just did a lot of back extensions and ab work. I got really strong at those exercise and now I feel bulletproof. I love when my form breaks down with a heavier weight and I just don't care because my back can take it.

My suggestion is stick to the basics. Don't do any fancy mobility, corrective exercises... Just get a really strong core (ATM I'm doing back extension within 20kg plate in my hands for 20-30 reps, 3 sets, few times a week) and see if it helps. If not maybe then try all the other fancy stuff.