Thing is, you have no mark as read anywhere on the forum on latest lists.
You only get that in “unread” and “new” tabs, there is a feature that is missing that means you can not “dismiss new” when you are filtered into a category. You can dismiss “unread” when filtered.
I am fine to add a dismiss “new” for when you have “new” selected in a category it is not implemented yet cause it is a bit tricky.
That said, I don’t think this really would help your particular workflow that much at all cause you would have to visit “new” in the category, hit dismiss and then visit “unread” and then hit dismiss.
What it feels to me you are asking for is a mixed “unread+new” list that you can quickly clear off. You already have the last visited line you can rely on which is 100% automatic and gives you similar behavior, so when you catch up on a category you only have to read till you see the “last visit” line.
I worry though that you did not think through this request properly.
If you “cleared” stuff off, do you want Discourse to remember your position in the topic when you eventually re-visit it? Or do you want discourse to skip all the posts you did not visit?
A “strong” clear like we have for “dismiss unread” can cause confusion. My guess here is that all you are asking for is a way to turn “links” on the page from “BOLD” to “not bold visited” on demand and keep all the tracking in tact. I worry that adding such a feature would cause a lot of confusion.