Note: this should work for any input that sway recognizes as a tablet input device that provides absolute position instead of relative.

In desktop environments like KDE, there is a fun GUI to help run this. However, in sway, you need to do this manually.

You can view a list of inputs to make sure your tablet is detected:

swaymsg -t get_inputs

Map the output using swaymsg:

swaymsg input type:tablet_tool map_to_output DP-2

where DP-2 is the display to map to. Input type tablet_tool should match all tablets.

I have a video of this I should upload…