I have no idea how Puppeteer handles this but Playwright has a little section on Chrome within Docker: https://playwright.dev/docs/docker#run-the-image

Basically, the Chrome sandbox needs a non-root user as well as a different seccomp profile configuration. No idea if this helps or if you already tried this but it’s worth giving it a shot.

Which I just now (after posting) noticed was already mentioned in a different comment. Sorry!

One more thing I just noticed: when you long-press the floating action button in the feed, there’s a “Dismiss Read” option which seems to remove all read posts from the feed. Although you have to trigger it manually, it might be good enough?

Edit: And I can do you one better, I think: Go to Settings, Account and disable the “Show Read Posts” option. Because as it turns out, this functionality is built into Lemmy.

Interesting, that indeed doesn’t seem to exist. Best workaround I can suggest would be to enable gestures and then assign the hide action to one of the gestures.

As a former Sync user, I can wholeheartedly recommend Thunder.