I did actually unfollow ~95% of my friends once but then found myself in that situation where suddenly Facebook became interesting again I was checking it more often. I recommend the opposite and follow as many friends from high school and work as possible (assuming you don’t work at a cool place).
Try practicing doing nothing I.e. meditation and see how that goes. When I have nothing particular to do my mind needs some time to make the switch from that mode where it tries to distract itself by coming up with new things it wants to do until finally it reaches a state where it is calm and steady. I consider that state the optimal one to be in since only then my thoughts are directed deliberately at neglected and important issues rather than exercising learned thought patterns.
I suspect doing long-term (or any) studies on people diagnosed with depression and weightlifting would be difficult, since the motivation required to do regular heavy exercise is either preventing people from following a strict routine or it would disqualify them from the clinical diagnosis of depression. I have tried exercise as part of my life-long battle against depression and in a recent conversation with a therapist was told that I am in fact not depressed, because a depressed person "is not be motivated to invest effort into doing something about their depression".