@MrStevns I tested MyPaint latest development build and had a similar issue as @kaiko with the pressure sensitivity (no pressure)
What I did to workaround was to change the Windows compatibility mode form Win 10 to Win 7, and it worked again.
That said the last build that was working without this workaround for my system was pencil2d-win64-2020-04-04.zip as the whole batch between April 13th and may 3rd has the original brush system for some reason, and it starts to lose pressure sensitivity from pencil2d-win64-2020-05-09.zip onwards.
I feel that whatever you merged into the MyPaint branch after the April 4th version from master, is the culprit for this behavior in both Pencil2D master and in this branch.