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:

• Connect
• Eternity
• Interstellar
• Raccoon
• Summit
• Sync
• Tesseract
• Thunder
• Voyager

Do NOT support keyword filtering:

• Alexandrite
• Jerboa
• Lemmy UI
• mlmym
• Next
• Photon
• Quiblr

Comment anything I have missed or mistakes I made

https://feddit.uk/post/18770058

Voyager

boost! used to be a reddit client but is now entirely lemmy

Adding more to the list:

Sync, Thunder, Summit

Voyager does keyword filtering. It's been awesome since the shit stain won, kept my feed to more sane/less doom scrolly content.

Boost

Voyager does this

Connect has title, community and domain keyword filters, works pretty well.

lemm.ee##div.post-listing:has(span:has-text("/Trump/i"))

Put that into your adblocker custom filters. Just change the lemm.ee to lemmy.world (or what ever instance you're on)

I use Thunder on iOS and it says it’s available for Android too. It has filters and I have them set to exclude just about any word I can think of that has to do with US politics. I haven’t seen a post about that yet so I assume it’s working.

Eternity does

I'm using Voyager and it handles that pretty well.