I sit in a car 9 is hours a day. I know your pain.
That being said you are fighting a mountain so consistency is your friend here.

Mobilize before and after work. Focus on hip extension. I do the squat prep hip opener, couch stretch, and t spine extension. on occasion I found the cook hip lift.

After work I hit a little couch stretch, rectus/ psoas/ql/smash.

Don’t forget about the things you can control. Drink plenty of water lightly salted, wear compression socks, move and stand whenever you get the chance, make sure your warming up and going down before and after your workout, be as active as you can be the rest of the day if you’re sitting that much find a way to get some walking in non exercise physical activity is your friend.

I keep a handful of balls with me in my car to smash while I’m driving (One supernova and too hard rubber balls about the size of the small supernova.) Obviously that may not work out so well if you crash while mobilizing. Not sure what would happen but it’s probably not good so don’t do that.