Pilates with a physio was surprisingly effective if slow (noodle person). I lost it all over the time we don’t talk about and can’t really regain but it’s worth a try if you can afford it or get it covered.

Some years ago, I did Pilates once a week. It was great for tone and flexibility. I don’t know if it specifically helps with posture, but you know that wobbliness that you can get trying to do a slow controlled movement? Its good for that kind of stuff. It does take time and consistency though, not a quick fix. A lot of posture problems can come from lack of core strength, both Pilates and yoga would be good if that’s where the issue is.

I am currently in peak hunchback phase but previously I've done well with both gym (super simple jog + upper back and shoulder machines) and yoga. Yoga I like because it builds strength but if taught well also helps your nervous system so you aren't holding on so tight. I've not been back to a studio since they all got so expensive after COVID but there's good YouTube stuff. Yoga with Adrienne is probably the most popular absolute basics and she usually has a 30 day challenge in Jan.

Edit for spelling

yes, the gym is great as you have a coach/instructor

I suggest getting a gym buddy , they help you with getting exercises right and with motivation

also having a regular habit helps