In case it helps in narrowing it down.
I have the wacom tablet connected via a USB switch. If I switch the hardware to a Kubuntu system running GIMP 2.10.30, it works fine.
The failing system is a "dev box", so if you want me to try a number of versions (and give brief instructions) I can do that.
As I said previously, the failing system just moved from bookwork to trixie, I'm afraid I didn't note the (working) gimp version prior to upgrade.
-- Graeme
