Can one use present continuous to describe tendencies, such as:
Oh this word? It's not being actively used these days anymore.
This sounds good to me, but I can't find a grammar rule to support this.
Will people understand that? Yes, but people would generally say or write:
Oh, this word? It's not used anymore.
In your sentence, the adverb "actively" is extraneous. Is there a way for a word to be inactively used? No, there isn't. Also, "anymore" already expresses what "these days" expresses, which makes "these days" redundant.