The magic sauce is here: https://askubuntu.com/questions/1511654/how-to-make-balena-etcher-and-other-appimages-work-in-ubuntu-24-04
Once I had done this, and upgraded to the latest version of ART, all was well.
My other Electron based apps and AppImages all work fine, except for FreeCAD, which doesn’t run under Ubuntu 24.02 either.
They are aware of the issue. It’s fixed in the dailies, but not the stable.
Again, thank y’all.
Chris