The suggestion elsewhere to sign out of Creative Cloud desktop app, then sign back in again, worked for me. And, it's not enough to just Quit CC desktop & then re-open, you have to go in (Tools, I think?) & deliberately sign out. You're then immediately prompted to sign back in, & now the new LR app is launching. Taking some time to update a catalog of 83,000 images, though.
thank you a million, Bob - this worked for me!