I liked Ready Player One and wanted to know if asking for related books would be on topic or not. Is it?
(Have not used this SE in a while)
No. Such a question would be entirely off-topic and would be closed in very short order. Per the FAQ
Not all questions have a home on Stack Exchange. Please note the following types of questions are off-topic here:
Reading or viewing recommendations: I liked X, what should I watch next?
As @Valorum wrote, asking on SFF.SE is off-topic per FAQ, however, you can still use the advantage of the many fantasy/science fiction enthusiasts and ask for book recommendations in the main chat, The Restaurant at the End of the Universe.
I did so myself previously and got a few good recommendations of fantasy series.