So two things to add to what others have said.
One, compression socks are a game changer especially for longer flights. Helps me a ton.
Second, this might sound weird, but do you have your tonsils and have you had a lot of cases of strep throat? Both me and my sister both have had our tonsils out as adults and it basically magically cleared up a bunch of joint pain I had.
I used to have excruciating knee pain if I sat still too long. Like I almost collapsed getting out of the car once cause I had dozed off for an hour or two and it made my knees hurt so bad.
Now I don’t have nearly the issues. It’s something to do with strep liking to basically hang out and cause inflammation in your joints.
I’m not gonna lie to anyone reading this though, getting your tonsils out is fucking miserable… When I went back in for my post op checkup the nurse said they had a patient earlier who had a purple heart and he had apparently said he would have preferred to be shot again over having his tonsils out.
Still worth it in my case anyway (not just the knees, had an infection and tonsils were giant, inflamed shit heads that kept causing issues)
That sounds real similar to what I was experiencing. Might be worth checking if you are a strep carrier, some people can have it without symptoms. Definitely no guarantee that it’s related but may be worth looking in to.