General advice for prolapse safe exercise is to avoid anything that increases intra-abdominal pressure (so yes, probably no sit ups for this reason, or Pilates exercises with both feet off the floor at the same time. Heavy lifting, chin-ups, plank etc also not great), and anything high impact. But the most important thing is to pay attention to what makes your symptoms worse, as intra-abdominal pressure with different movements varies loads from person to person.
It’s also worth talking to your physio about running and lifting if that’s what you want to do - I have a grade 2 cystocele and slight uterine prolapse but used to run to manage anxiety and depression, and gynae and physio are both supportive of aiming to get my pelvic floor strong enough to return to running reasonably comfortably because the whole-person benefits outweigh the prolapse risk. With this in mind, I’m doing Pilates to work my pelvic floor in the context of my whole core/body (instructor is a qualified physio and aware of my prolapse, and lets me know how to modify where needed), electrical stimulation to ‘wake up’ damaged pelvic nerves and strengthen pelvic floor (under supervision of hospital physio), and kegels (4 sets of 10 slow and 10 quick daily using the NHS Squeezy app to nag me). Am also waiting for a pessary fitting in case that helps - can report back if you like?
There are some good prolapse related episodes on ‘the pelvic health podcast’, and some useful workouts if you search ‘femfusion fitness’ on YouTube. Haley Shevener is inspiring if you’re on Instagram (and swings some impressive kettlebells about), as are Pelvic Floor Patrol (lots of info and resources)
Sorry for the essay, and hope at least some of it helps.
Also, my prolapses both go up and down a bit according to my hormones/activity levels/their own nefarious agenda so don’t panic too much unless it’s permanently got lower. Lying down with hips propped up is a very old school treatment, but does give relief of stuff feels really bulgy/draggy).