The JTAG2UPDI firmware sits on the Uno board, so when you select a port in tools> port, the Port (COM24 in my case) is described as 'COM24 (arduino uno)'.
As I mentioned, the settings work fine to upload code to the AVR 4809 in Arduino IDE 1.8.13, but I'd like to have the benefits of IDE 2 if possible.
I've probably missed something somwehere in the IDE 2 / JTAG2UPDI install / setup perhaps?