If you really want entire lemmy instances to be 100% meme-free, the mods would have a lot to do because they'd have to read through every last post and comment.
Just like not every picture with text in white Impact with black outlines is a meme (it has to be established as such), memes aren't only pictures with text in white Impact font with black outlines. In fact, they aren't always pictures. They can just as well be text, embedded in other text.
Any catchphrase can be a meme. Snowclones are memes, too. Snowclones are the memes of the analogue era. They date back to the analogue era, to the mainstream media of the 1970s, the 1960, the 1950s, as far back as William Shakespeare, as far back as ancient Rome, and I'm pretty sure there are snowclones from ancient Greece.
I can't imagine the mods of any one Lemmy instance reading through all posts and all comments and sanctioning everyone who has dared to use a decades-old snowclone in it.
(Whoever finds a meme in this comment may keep it.)