I read this a month or so ago... Or thereabouts.... I liked it. Been a Heinlein fan all my life. Came out in March, I believe. Fun look back at earlier works by other authors’ famous series like, Burrough’s Barsoom and Doc Smith’s Lensmen series. It’s his parallel universe concept here... Where everything ever thought of actually exists somewhere in a parallel universe..... Great romp!
Speaking of parallel universes, my favorite references to RAH is in the story “The Return of William Proxmire”:
“Admiral Heinlein won’t let the Russians have Spaceships...”