Why do you get to arbitrarily define what constitutes as a mental illness despite having no education, training, supervision, or license in the matter?

Same reason I don't need formal training to know the guy on the sidewalk shouting that he's the reincarnation of Jesus Christ is mentally ill.

Gender dysphoria has been described in the literature

This may shock you but most things libsoftiktok posts aren't true. Try going outside, you've got terminal conspiracy brain.

This is actually a great example, because it is a reflection of your ignorance of mental illness. There are many reasons why someone may be doing that, such as substance use, emphatic spiritual belief, medication side-effects, etc.

Gender dysphoria is a specific experience, and is not synonymous with "being transgender".

This is classic.

All of which are causing mental illness, whether its chronic or acute, it doesn't matter to me. The person is exhibiting a clear and definable sign of mental illness that's easily recognizable.
If a person is babbling incoherently and spraying feces over a room while ripping chunks of hair out of their head, I, the observer, have no difficulty identifying them as being a wackadoodle that is off their rocker. I don't need their life story or whether their immediate episode was triggered by some deep seated trauma or a blow to the head or just doing a whoooole bunch of PCP.

No, actually, that is not how that works at all. It's okay, I understand that you're a layperson without any formal education or training in mental health. Too bad that understanding isn't mutual.

Logic, reason, common sense, intellect, rationale, etc