Mental issues are genuine conditions--what is this "or" you're talking about? Also, the existence of a debate doesn't mean that the issue isn't pretty clear (or doesn't have some clear parts that are still "debated"); it could also mean that one or more sides is too ideologically driven to pay attention to evidence.

In this case, the papers from the Amsterdam gender identity clinic are, indeed, pretty clear. (They can't address whether trans identity is over-diagnosed, under-diagnosed, or diagnosed-with-a-multitude-of-errors-in-both-directions in other countries, but they can and do pretty clearly document a long-lasting condition of gender dysphoria that is often relieved, and for fairly long periods of time, by gender-affirming care.) They're not remotely the only ones, but they take a very thoughtful approach, so are generally the ones to read first.

There are lots of open questions, but "is there even a genuine issue" is not one of them.