I had a client side feature like this in Slide for Reddit. I must admit, I miss this capability quite a lot.

I’m missing this from RES. “day x of posting y until-” ZAP

Not sure if helpful but Boost for Lemmy has this feature. It’s called “Muted Words”.

Voyager seems to have this feature idk for sure but i think eternity does too . And they both are foss and doesn’t contain adds or tracking .etc.