Did you find a way to export all the UDIMS of a texture?
Adding an offset to the UVs I managed to specify what UDIM to visualize, then I could draw the material to a Render Target and export each UDIM one by one.
This is definitely a hacky way of doing it since there is a lot of quality loss in the exported Render Target.
In my case, I only needed to use the UDIM textures as a reference, so this method was enough for me, but it would be nice to be able to export them properly.