Sadly they're gone.
It wasn't a feature I used much, but some of them were really interesting and original. And it was a good community contribution.

Yes, they have been gone for a long time now. GOG didn't like them, after all, because they had no control over them. And they weren't replaced by anything else.

And MaGog, the search engine that could be used to find all sorts of games, has been shut down too, because GOG started selling DRM-ed games and the creator of MaGog felt no desire to keep supporting GOG with such a lot of work. Which I totally understand and agree with.

I suppose the community could maintain some lists of topical games through forum threads or externally.

I thought "curated collections" on the front page from various publishers/YouTubers/etc was the replacement. You mean to tell me you'd rather have user-generated lists of which games include DRM schemes and are unsupported by the dev/pub, instead of having Slitherine or whoever tell you what to buy?

I see. I always thought steam nicked the idea of game lists (ie steam curators) from GOGmixes. Sad that GOG itself abandoned them when it was a feature that added curation and GOG is touted as a curated store.

What did the creator of MaGog say?

I closed down MaGog on 1/1/21 because, just like Lifthrasil said, I don't like the direction GOG is going in and I don't want to invest my time in making it easier for myself and others to buy games here, which is what MaGog did, among other things. That's also the reason I have joined the boycott here: https://www.gog.com/forum/general/boycotting_gog_2021.