I also has a spinal fusion and bone graft (across my low back) the old way (not with lasers) 20 years ago and it caused thickened scars and some are keloids. I’ve also had abdominal surgery and that scar can get itchy and ache.

I’ve had success getting my keloid type scars treated by a dermatologist. She prescribed topical clobetasol steroid gel. When that causes too much thinning of the skin, we switched to injections and it really helped with the itching. I think that would only work for a keloid though.

My other scars are what my PCP calls “reactive,” meaning they have altered nerve sensations. Scar tissue can go pretty deep and stack
on top of the tissue and keep stacking so that it pulls on nerves and tissues creating itching or really deep aching pain.

For those, my PT taught me “scar manipulation” techniques. They’re similar to this (it’s from a breast cancer page but it’s the first thing that came up and it’s the same idea):
https://myhealth.alberta.ca/breast-cancer-surgery/at-home/scar-massage
She also taught me scar desensitization to help with the irritation type sensation you’re describing with your shirt. That involves taking different materials and running them over the scar. For example, you can start with something soft and smooth like a tissue and rub it back and forth. When you get used to it, or if that’s too easy, move onto something with more texture. In that way, I was able to get used to the feeling of clothing on the scar.

You could either look up scar manipulation and desensitization techniques online and try them. My pelvic PT taught them to me. A dermatologist might also be able to help if something like the injections they use for keloids might help.