Warnings in general weren’t a thing in a lot of these spaces. Sometimes, people would be mad about things that were permanent like character death, but trauma followed by a happy ending just wouldn’t have made that list a lot of the time. I don’t believe romance novels were relevant. The lack of a concept of trigger warnings was. (The actual term seems to hail from the mid 00s, for example, though obviously, warnings existed prior to that.)
The biggest change was the advent of tags existing.
Technologically, they’re not a thing on the old internet, and metadata tends to just be sparser in general. Some fic archives did start to have some filtering, but it was pretty basic and varied a lot by space.
Keep in mind that for much of the 90s, the shape of a fic archive was a hard-coded html page or maaaaybe that X-Files FTP site. They looked fundamentally different from the more recent type where you upload things yourself and you can edit in a WYSIWYG interface.
I think the main driver of internet metadata is generally porn, and I don’t mean fandom. I mean commercial porn. This is likely a big driver for being able to sort anything at all by tropes. I couldn’t point you to exact moments that moved tech forward though.
