The iMac Pro has a TDP of 140 W. The i9-13900K has a TDP of 125 W (although it goes higher on turbo boost). Could I upgrade the iMac Pro to have the 13900k? Is the TDP the only factor that matters when upgrading CPUs?
Can't you get socket adapters though? I thought I saw those somewhere...In short, no. A 13900K isn't going to fit in any Intel Mac model. The 2017 iMac Pro had a Xeon-W with a LGA 2066 socket, and even the last Intel iMac (the 2020 with 10-series chips) had a LGA 1200 socket. The 13900K and 14900K are on LGA 1700.
Aside from the sockets, the chipsets also wouldn't be compatible. Intel typically swaps sockets/chipsets (in terms of compatibility) about every two "real" generations. The 14-series is really a refresh of 13-series (both use Z790 chipsets), and both are compatible with the same LGA 1700 socket with 12-series CPUs and the older Z690 chipset (needs a BIOS update).
No (those existed a long time ago, but not anytime recently), and the BIOS wouldn't know what to do with it even if it somehow electrically connected (also unlikely because these recent generations use a huge amount of power and need many of those pins for power delivery).Can't you get socket adapters though? I thought I saw those somewhere...
And again, I'm sure you could do some hackintosh-y stuff to make it work.