A trademark isn't "you don't get to use this word because I own it now", it is "you don't get to use this word in this context as it is confusing". If you want to name your restaurant Ludwig, go ahead: you just can't name your filter Ludwig. With the exception of Lo-Fi, where maybe you could make a defense, these names are non-obvious and have never been in common use to describe a set of modifications to photographs. Just because Clarendon isn't a unique word does NOT have ANYTHING to do with whether or not you could trademark it for something.
You can't just say "durrrr... I've heard this word before!" you have to actually show that that word has been connected to that context and isn't some otherwise unique usage, and I simply don't see how you are going to claim that for these words: if you show those filters to people and ask them to describe them, the only reason they would say "Clarendon" is because of Instagram's prior usage carefully associating that word with that filter behavior: if you believe otherwise you have to show THAT, not that the word itself has been uttered by someone in the past.
Why is it confusing to use “Ludwig” as a filter? Nobody is going to get confused what site they are on based on the name of a filter. In fact, it’s less confusing than having to rename filters for each product.
I get that it's about context. But to me this is meaningless, why should any company be able to restrict the usage of common words in a business context?
As a sidenote, Lo-fi has definitely been used in the context of photography before Meta decided to use it as a filter.
I’m afraid you may have some misapprehensions about how trademarks work, and I don’t think this is about trademark specifically anyway.
Trademarks do not give someone the exclusive rights to that word in all contexts. Instead, you register a word or phrase and an category. For instance, there are about 1500 trademarks on the word Apple, from laundromats to eyeglasses[0]
But Meta’s complaint here doesn’t seem to be trademark; companies don’t typically trademark every name like filters. But there is lots of other IP law, including trade dress, which is different from trademark.
And much as I love the fediverse and hope it displaces dinosaurs like Meta, I’m surprised anyone would defending taking the filter names em mass and using them to refer to the same visual effects. That is not something one does. Meta is not claiming ownership of all uses of those words in any context, they are saying please don’t rip off the exact words to clone their UX.
You can say the same for Apple. I think the trademark applies when a common word is used in a distinct business case. Here the word is used as a filter name, for instance. That application is unique.
Juno, the ancient Roman goddess, a word in use for over 2000 years.
Clarendon, the wikipedia page at https://en.wikipedia.org/wiki/Clarendon lists approximately 40+ different uses, from place names to typefaces.
Lark, well, do I have to add anything here?
Ludwig, uhmmm, Beethoven's estate is about to be sued?
Lo-fi: Yes I never heard of this word before in the context of photography. True originators.
Please stop the trademarking of common words and cultural heritage that belong to all of us.