Rather than using a sensitivity filter I’ll just clearly mark manga-like memes as Art/Meme.
If I’d mark this post as NSFW even more people might thought of it as a spoiler. You click expecting something lewd, find manga panel then it must be a spoiler right?
Anyway I guess there are a lot of different reactions to spoilers. For me seeing a panel of something I know it’s going to happen it’s not a big deal because when you know what’s at the end then it’s all about the journey. That would count as a minor spoiler easy to ignore. But if the panel contains something so unexpected as idk main character death or something like that I’d consider it a big spoiler.
As for whether something is a meme or source I guess I just spent too much time on the internet to the point I didn’t even thought it could be source material. Then after your comment I went from 100% meme to like maybe 99% meme.

Btw since Lemmy doesn’t have spoiler tag I recommend you blocking !dandadumber@ani.social if you haven’t done that already. It’s a community for dandadan manga and it can also pop up in your feed.