External Wacom One tablet on Linux
The WacomOne tablet is well supported on modern Linux distributions, it seems to be supported in Ubuntu 20.04 and probably also Ubuntu 18.04 LTS.
Some things you may run into though...
Stylus mapping doesn't match the Wacom One screen
This is probably trivial to someone who knows how X11 works, but for non-expert users it can be a bit tricky to figure out.
The information below is probably old and now has been integrated in the plasma system settings, if you go to System Settings -> Input Devices -> Graphic Tablet Go to the "tablet" tab and select the button "Map tablet area to screen". In the upper left of the pop-up window, you can toggle which screen the tablet area is mapped to.
Copied from: KDE forum (I'm not sure if this is true for Gnome as well, or on Wayland systems)
$ xinput # get the IDs for all relevant pieces of my tablet. ⎡ Virtual core pointer id=2 [master pointer (3)] ⎜ ↳ Virtual core XTEST pointer id=4 [slave pointer (2)] [...] ⎜ ↳ Wacom Bamboo 16FG 4x5 Pen stylus id=17 [slave pointer (2)] ⎜ ↳ Wacom Bamboo 16FG 4x5 Pen eraser id=20 [slave pointer (2)] ⎜ ↳ Wacom Bamboo 16FG 4x5 Pad pad id=21 [slave pointer (2)] ⎜ ↳ Wacom Bamboo 16FG 4x5 Finger id=22 [slave pointer (2)] ⎣ Virtual core keyboard id=3 [master keyboard (2)] ↳ Virtual core XTEST keyboard id=5 [slave keyboard (3)] ↳ Power Button id=6 [slave keyboard (3)] ↳ Power Button id=7 [slave keyboard (3)] ↳ Microsoft Microsoft® Nano Transceiver v2.1 id=13 [slave keyboard (3)] [...] $ xrandr # get the names of my displays Screen 0: minimum 8 x 8, current 3840 x 1200, maximum 16384 x 16384 DVI-I-0 disconnected (normal left inverted right x axis y axis) [...] DVI-I-3 connected 1920x1200+1920+0 (normal left inverted right x axis y axis) 546mm x 352mm 1920x1200 59.95*+ 1920x1080 60.00 1680x1050 59.95 [...] DP-1 connected 1920x1200+0+0 (normal left inverted right x axis y axis) 546mm x 352mm 1920x1200 59.95*+ 1920x1080 60.00 59.99 59.94 50.00 60.05 60.00 50.04 1680x1050 59.95 [...] $ xinput map-to-output 17 DVI-I-3 $ xinput map-to-output 20 DVI-I-3 $ xinput map-to-output 21 DVI-I-3 $ xinput map-to-output 22 DVI-I-3