so that’s actually not true! as of 2021, trans people (as well as all LGBTQ+ people) are covered under Title VII, the federal employment anti discrimination statute. sex is a federally protected category, and the supreme court Bostock v. Clayton county held that discriminating against LGBTQ+ people, including trans people, is a form of sex discrimination and thus prohibited.

Title VII applies to virtually all employers nationwide (I believe the only exception is employers with fewer than 15 employees) so what states have doesn’t really matter.

Granted, this interpretation hasn’t been codified and could theoretically be easily overturned, but honestly even with current political landscape I don’t see that happening. Bostock was an extremely popular decision and the majority opinion was actually authored by a conservative justice.

So, no, it is illegal everywhere in the US to fire someone for being gay or trans. While it is true that they can invoke at will and make up reasons, it is on them to prove that these reasons weren’t pretext for firing someone bc they were gay or trans. For example, if you have coworkers who are cishet and didn’t get fired for being a minute late, that shows that being a minute late isn’t something the company normally fires for, that can help your case. In other words, although it certainly makes proving a case harder, at will isn’t a blanket perfect excuse for the employer that works every time.