It is extremely important that tablet settings should default to preserving 1:1 aspect ratio. They currently default to something ablative.
Affected version
Debian, GNOME Shell 3.38.5, X11
Bug summary
Tablet settings' "display mapping" currently defaults to transforming the tablet inputs to stretch over the screen dimensions. No artist would ever want to use a tablet in this mode. Having the tablet default to that mode can cause them somewhat serious setbacks when the screen ratio is close to the tablet ratio, it will mess them up but it wont be obvious to them why, and they may just blame themselves. The setting should default a 1:1 aspect ratio. This setting is available, but for some reason, isn't the default.
What happened
Currently, in the settings for wacom tablets, under tablet settings, there is a setting that determines how the position of the tablet pen maps to the position on the screen. The default setting transforms the tablet inputs to fit the screen, squashing the X or Y axis to fit. There's another option (and this is the correct option) to maintain the aspect ratio of the tablet, but to have some of the tablet letterboxed off from accessing the screen. This should be the default. The impacts on the user of this not being the default can actually be pretty awful. I'll tell you what happened in my case.
Most people who draw learned on paper. On paper the aspect ratio is 1:1. If you have a different aspect ratio on a tablet, they wont be able to draw properly. Every line they draw will have the wrong angle. If the aspect ratio of the screen and the tablet are close, they might never understand what's going on. They will think that they are the problem, they'll think that they just need to adjust to the new drawing tool. They'll relearn how to draw with the scaled aspect ratio. This will be an arduous process, at minimum. When they switch to another computer with a different aspect ratio, they'll have to repeat it all over again.
I can't imagine how much damage this would do to someone who is learning to draw for the first time on a tablet with the wrong aspect ratio.
One of the reasons they wont suspect that the problem is the tablet aspect ratio is that they wont be able to imagine why a desktop would would ever allow a tablet to be used with a skewed aspect ratio. No artist would ever want to use a tablet in that mode. There's no use for it.
For me, the dimensions of the tablet and the dimensions of the screen were close enough that I kinda had no way of knowing that this was the reason I was having so much difficulty acclimating to the tablet. It didn't occur to me to check until a friend mentioned their linux installation having this terrible default in a much more conspicuous way on their multimonitor setup.
What did you expect to happen
Default to using a 1:1 aspect ratio. If switching to requires manual involvement for some reason I can't imagine, then refusing to support the tablet until the user manually calibrates would still be preferable to the skewed default (at least, it must in the cases where the screen and the tablet dimensions are close but different, which is when the confusion occurs.).