Not on trigger warnings, but on content warnings on general. It folds the post by default, but shows the warning description so it's useful for lots of reason.
For example "USpol" is often used as common CW but not specifically TW. But it could be "boob", or "giant spider", or "furry", or "food photo", or "super long post" whatever else you think people may react to with "I wish I didn't have to see that while scrolling the timeline". It's really just about making it a nicer place to others. It's common, but it's not like people expect you to put USpol warning on posts from account which deals only with politics.
On bluesky, the self-applied user moderation is abused in a similar way to hide spoilers.
If you post an image, you can tick the "Adult Content" box and it has that label applied to it. It's the only way to do that currently.
That makes sense, thank you for explaining