Like you, I’ve visited many times and done all the tourist things I think I want to.
But there are a few that may be ‘less’ visited -
Sir John Soane’s Museum is an extraordinary personal collection amassed over a lifetime. https://www.soane.org/
The Horniman Museum and Gardens, another amazing and eclectic personal collection. Horniman was a tea merchant who traveled the world and brought things home. Lots of kids’ stuff at the museum. https://www.horniman.ac.uk/
I went to the Science Museum last Feb for a special photo exhibit - Amazonia. Not sure how long it will run, but the Science Museum is amazing for the scope and breadth of what is there. (And the V&A across the street.)
Lots and lots on the internet now about the architecture of the various Underground stations. Lots of links on google search. I visited the station that is supposed to be most like the Moscow underground a few weeks ago - Gants Hill on the Central Line
And I found an Asian food court - about as close to Singapore or Taipei as you can get - Bang Bang Oriental Food Hall https://www.bangbangoriental.com/ - way out on Edgeware Rd.
Enjoy!