Exercise is good for mental health

Update:19 Feb 2021

The researchers found that people who exercise regularly feel bad for an average of 35 days per year, whereas inactive people feel bad for an additional 18 days.

From the study:
Individuals who exercised had 43 percent fewer days of poor mental health in the past month than individuals who did not exercise but were otherwise matched for several physical and sociodemographic characteristics.
All exercise types were associated with a lower mental health burden.
The ideal amount seems to be three to five training sessions per week, lasting 30 to 60 minutes each.
But the takeaway should be that any amount helps, so don't stress about hitting that perfect balance: "All exercise types were associated with a lower mental health burden than not exercising."