As quoted from another, but still related thread: Gold said: Roll20's staff announced at Roll20CON last weekend, a version of what you're asking is coming, on the horizon. It will be called "Page Categories" and will have functionality matching both tags-tagging, and Folders. It's
been a popular suggestion over the years, so there are other Threads
for this topic too, but the good news is Roll20 Dev are working on it
actively. I hope so, I'll believe it when I see it on the Dev server.