Yes, questions asking about online resources are on topic. There is nothing that makes them off topic; contrary to the tag wiki they are not categorically and inherently about recommendations. The tag wiki doesn't accurately reflect usage of the tag, and is from the year before game recommendations were ruled off topic; I'm updating it (see end of post).
They contain a lot of recommendations, but that's just because it's one of the things people asked for recommendations of. The fact that online-resources contains a large proportion of a no-longer-accepted question category does not make it synonymous with that category.
- Where can I find the various D&D 4e web articles? (If they even still exist.) — not a recommendation, it's asking how to navigate WotC's site to find material after a site migration.
- How can I continue to access Wizards of the Coast's D&D 3.5 Web articles? — same again.
- Are the WotC archives of d20 Character Optimization forum forever lost? — asking about the impact of the WotC forum closure on key community resources.
- Where can I find a complete timeline of the history of Points of Light? — not a recommendation. It's a community-compiled resource that exists but which I lost track of (much like The Rules of Hidden Club); I asked about where it's currently located. It was found and provided.
- Are there any Handbooks for the "Expert" NPC Class? — not a recommendation. The D&D 3.5e optimization community has compiled a number of guidebooks/handbooks on optimizing certain classes. Any given class has a small number (as low as "just one" or "none") of such handbooks that the optimization community recognises as the standard go-to; this question was looking for what they were for one class after being surprised they couldn't actually find any.
- Where can I find an exhaustive (and constantly updating) list of 5e reference and adventure books? — not a recommendation. There are a number of products connected to this game; the author was asking where we find them actually listed and collected together. Such a library exists and was provided.
- Where can I find a proper library of free adventures for Fate Core and Accelerated? — same again. There are three key libraries and they were provided: Evil Hat's own, the Drive Thru RPG store through which Evil Hat distributes electronic versions of their games, and RPG Geek which is effectively our hobby's Wikipedia.
Concerning those last two, let's recall that a definitive part of recommendations is that we are bringing to the asker a variety of suggestions for things they could use in hopes of finding a best-fitting one. They ran afoul of "every answer is equally valid". Here, providing what is factually the canonical resource is not a recommendation of something equally valid, it is the correct answer. These are like content-identification or product-identification requests. An answer that says "use this" is not, inherently, a recommendation.
I've updated the tag wiki to the following:
for questions about using or finding online resources. (Recommendations of "best" resources are not on topic, but we can provide guidance around identifying canonical resources.)
This tag is for questions around using online resources or identifying canonical resources.
Recommendations for game materials are now off topic, but we can provide guidance around the existing canonical resources available.