Mostly stretches. The key point is to just move. Get up, stretch, walk around. There’s no specific exercise really. Your body is a series of pulleys and levers. Try not to think in isolated terms when it comes to muscle structure. You can’t workout your biceps without also working out your triceps (they are opposers). Whatever you do affects your entire body.

With that said, hanging is amazing for your back. If you can hang for a min or so couple of times a day (morning and before bed), it will decompress your spine and combat the effects of gravity.

I like the youtube channel Minus the Gym's video on stretches to do to undo sitting. Hope that helps.

A really simple and effective solution is walking. It can not be overstated how helpful a couple short walks a day can help. You'll get the added bonus of fresh air, vitamin D and an opportunity to reset your brain. Quick and easy.

I'd focus mostly on hip mobility/flexibility, as the hip is the area that's most affected by sitting for too long. Just look up "best hip mobility stretches". Also, I'd pay attention to your back and find some stretches for it, too. I personally do that every day. I also walk 1 - 2 miles almost daily after work. That's another very good thing for your body. You need a lot of mobility. I also hit the gym 4 days a week.

I also recommend the Hybrid Calisthenics channel. He focuses on low impact, easy to get into training options.

https://youtube.com/@HybridCalisthenics

Just make sure you spend some time on your feet. Housework is good. Most smartwatches can let you know if you've not moved for a while.

Check out Dean Pohlman's "Man Flow Yoga" YT channel. He has at least one video, possibly more, that address this exact question.

How did we land on different "sitting too long is bad" videos on the same day. I came across this animated video which showed which parts of the body gets stressed when we sit too long this morning.

I like ChaseMountains. Some good exercises in there.

I was thinking about this by watching some streamers, some actually do a smart move and remove it the chair for some sessions. They use the PC standing, its not a bad idea, probably different if you sit behind the wheels.