Having finally fixed my laptop, I booted into Windows to try to get some work done.
However, since KB4505903, Windows had removed Sketchpad! You know, the only useful ink workspace app.

Unfortunately, KB4505903 was not actually installed (rather some later version), and I don’t have the time nor patience to figure out which later update to remove.

Bummer.

I guess I’ll try out the “replacement” app, Whiteboard.

UPDATE
Having tried Whiteboard… it’s not bad.

It has support for background colours and background patterns.
The toolbar is much more “visual” than last time, with brush icons for each.
Also the erasing is pretty cool - if you erase slowly, the erasing handle is small, but if you move quickly, the handle is large.

I do find it a shame that there is no fullscreen mode…