Imogen is Vulcan’s alter ego, who we normally see in the Monday slot, and I see from the app that Imogen last set the prize back in in 2017 and several times before that.
The theme was clear from a quick read through of the clues (very much my era!) and as a result the thematic solutions, including the hidden one, were pretty much write-ins. I feel for overseas solvers or millennials for whom this may all be a mystery.
I also came to a standstill in the SW corner at the end. It didn’t help that had the first word of 13d wrong, which is not something I knew and seems to be a historical term, not in Chamber or Collins, but it is in the OED.
I found it fun, not sure everyone will ;-)