I have a bipolar 2 diagnosis and seen a couple of people talk about needing to increase mood stabilisers on T as it affected them. I've been really fine on it so far... It made my depression harder to handle at first because it changed how I processed feelings, but I now feel more stable than I have in years. I think with some mental illnesses, anything can be a trigger to a cycle, such as seasons, caffeine, stress, alcohol, head injury, menstruation ect.
I sometimes think people put things down to testosterone when they could have other reasons. For example, I had an argument with somebody because she was going on at me a lot and being dismissive of my feelings and really competitive and I told her to stop and tadaaaa it's the T talking, not me being allowed to have feelings!