Ah OK, this is what works for me.
The “RP2040” sighting is for the Thonny interpreter selection menu, lower-right border, once the uf2 file has been installed, and then only for the Pimoroni Pico 2 W uf2 build (to be clear, not the Pico Plus 2 W).
I do not have a screen capture as I have now reverted to plain, vanilla MicroPython.
OK, all sorted.
No idea why I had the MicroPython(RP2040) interpreter rather than MicroPython(Raspberry Pi Pico) interpreter selected, not intentionally changed and as it’s been working OK for over a year with other Pico RP2040 devices, I’d not noticed it.
I started with a Wireless Plasma Kit (Pico W Aboard) - product page links to Getting started with Raspberry Pi Pico which does note - You’ll need have ‘MicroPython (Raspberry Pi Pico)’ selected as your Python intepreter.
So to repeat from my original post: adding current guidance to product pages would make getting started with a new device easier.
I agree. I have learnt to work with GitHub but a few pointers on where to look are always helpful.