I had a couple of bouts of depression during my masters degree which resulted in very bad grades. Is it a good or bad idea to mention this in PhD applications to explain my grades?
First of all, I hope you are doing fine now, have recovered from depression, or are on the way to recovery!
I believe that there is no need to give insight in your mental health to a possible future employer. I would advise you to generally speak about „health conditions“ instead of disclosing your mental state, if you feel the need to explain your grades.