Additional thanks to Lemmy clients that allow keyword filters unlike the default Lemmy UI
Regarding the post title: Lemmy itself allows you to block communities, instances, and users. But it does not support filtering by keyword, e.g. filtering out any post with the word "platypus" in the title regardless of where it was posted or by whom. With help from the comments below, here are some third party Lemmy clients that have their own implementation of keyword filtering:
Do you know if PieFed allows user-blocking of instances? Like allow someone to mention a community name such as firefox@lemmy.ml while blocking someone with a user account from lemmy.ml?