"I think it’s incredibly wrong, a total breach of privacy and an abuse of position for a police officer to put this on YouTube."
The police didn't do this. The bodycam footage was obtained from the police force in question by somebody making a Freedom of Information request.
In the USA, just about every public record can be accessed under either federal or state law. There are some exceptions though. For example bodycam footage will generally be withheld while the criminal case is ongoing or if it is inside somebody's home or the person is under 18 etc.
"...a total breach of privacy..."
I would totally disagree with you here. This happened in a public place (a university I believe). Now, if it had taken place inside this person's home then that would certainly be an invasion of privacy to release it.
"This person needs help not mockery."
Where is the mockery?
"And you OP - why have you shared it on here?"
There is, amongst certain sections of society, the belief that all trans-identifying men are lovely people who wouldn't hurt a fly.
This video allows us to see what happened when one trans-identifying man wasn't indulged in his beliefs.
It took two policemen to deal with him.
I would not want to confront a person like that on my own in a confined area.
"...a mentally ill person"
Is there any actual evidence of this?
If you have a look at the video, he looks like somebody who gets wound up very easily and is not good at controlling his emotions. Whether that makes him "...a mentally ill person" I really don't know.