[ivan1783]

Look into cycling, you have a big range of efforts you can do from barely anything to full out and you will any ways put some km's behind you. Its less impactful on the knees and joints in general, running is relatively hard on your joints especially if its on asphalt or hard surfaces. I also sit at a desk (not all day but any way a good part of it) and my go-to is cycling (road, gravel & mountain XC). Starting is easy, find a bike and start pedalling. When you get tired pedal less hard and go home. If you feel like you can do more do a harder effort or sprint, then bring it back to a slower speed, etc. Lots of videos available on youtube.

[bjowen]

+1 cycling. This is very contingent on the kind of area you live in (distances, hills, bike routes / lanes, general tolerance of cyclists) but it has made the difference between couch potato and relative fitness for a lot of people I know. The key for me and them is having it as your go-to transport for getting to the shops or school or the office. I think “incidental exercise” generally describes the approach.

[rsto]

I think this is good advice, except probably for road cycling. Both my physio therapist and Yoga teacher told me that sitting on a road bike is counter-productive to improving my flexibility, given that I already sit at a desk most of my day. Especially the hips will stay in the same angle for a prolonged time.

Edit: if OP is concerned about damaging their untrained musculoskeletal system, then swimming is a low risk activity to get started with sports.

[grvdrm]

Fair, but it’s best to view cycling as one component of a larger program that involves stretching and mobility to both improve your whole body and counteract the issues you mentioned.