These touchscreen with cases for 3B+'s are rather cheap so I’ve built a zynth . . .
or the other way up . . .
or much more interesting . . .
Much playing about in /etc/X11/xorg.init.d/
with the file 99-calibration.conf to get the touch screen to work properly. It boils down to adding the transform values after you have done the xinput_calibration to get the positions right.
My final answer to swap x & y needed . . .
Option “TransformationMatrix” “0 1 0 1 0 0 0 0 1”
so the whole files was … …
but it seems to work now . . .