Yes, which makes me believe that you are legally protected from being fired for publicly expressing your affiliation with a religious group. However, you are not protected from being fired for expressing political views, regardless of whether they stem from the religion you are affiliated with or some other source.
This is just an armchair lawyer level of reasoning on my end here, I have no idea if this is how it actually legally works, but that sort of makes sense. So if someone with the actual knowledge can chime in, that would be appreciated.
this whole cancel culture I think has taken a turn for the worse in the recent past.
Well yeah, but they can be, and their employer won't get in any legal trouble. Having controversial political statements on your tshirt doesn't mean that you will get fired or that you deserve to be fired, it means that your employer has a right to fire you for it with zero legal repercussions. And if the employer doesn't want to fire you for your political statement, they won't, it's up to them.
You raise an interesting point, because I feel like they would be fired for that indeed. What makes it interesting is that it becomes a political message wrapped in a religious statement, and I have zero clue as to how courts would approach that.
I think it just could be the case of a simple misconduct that has nothing to do with religious prosecution, because I don't think you would be able to get away with wearing a tshirt with a lot of really explicit and graphic quotes from the old testament at work, despite them having nothing to do with gender or politics (e.g., the example of Ezekiel 23:20 with very explicit content about reproductive anatomy of horses and donkeys comes to mind).