That's not true at all. There are many, many cases of people being banned for what I would consider quite mild transphobia. There's was a high profile case this year[0] where a republican Senate candidate was banned for saying,

"Women's sports are for women, not men pretending to be women"

It is not hard to find many more cases and of course the vast majority of banned accounts belong to people with no public profile and you'll never hear about them.

[1] https://www.pbs.org/newshour/politics/twitter-suspends-u-s-s...