Unfortunately, it's a huge thing. AO3 has a Ship Stat list that comes out every year and is posted on tumblr/reddit. Last year, Geralt and Jaskier/Dandelion was #5. Don't know what it'll be this year, but I don't really want to know at this point.
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The Netflix show is what kickstarted that and it's sadly leeched into a lot of Witcher discussion spaces, to the point where I've seen the books be dismissed as just "lore" instead of the actual source material because, y'know. Not enough Jaskier being gay for Geralt or whatever. There's also a few Witcher Shipping discords but I prefer to keep my eyeballs and sanity in tact than to check there for lulz.
All I know is Eskel was apparently a fujoshi favourite and his Groot-Fursona did not go over well.