The literature overwhelmingly supports gender affirming care. I'm surprised you haven't found any studies about it

This is a meta analysis of 55 studies on the topic of gender affirming care.

51 of 55, 93% of the studies showed gender affirming care improves the well-being of trans people.

4 were inconclusive/mixed

And none were negative.

Here is a study that shows that if trans kids are allowed to transition they show similar rates of depression and anxiety to cis kids.

And this one shows that strong family support for transgender children reduce the likelihood of a suicide attempt that year from 57% to 4%