On PC at least, go to your account settings and you can toggle 'Show read posts'. Untick this, and anything upvoted or looked at (looked at the comments, aka opened up) Will go away upon refresh.
This behaviour will carry over to the apps on refresh. It's quite aggressive though, so if you comment on something and want to check back on the activity you better bookmark it. But if you're like me , you only mostly care about replies to your comment :P
Yeah I’m a chronic post hider, so I neeeeeed it lol. Thankfully looking at images (by expanding them) also counts so it cuts down on upvoting/looking at comments. It’ll get there soon enough.