Comment 7 for bug 1900633

The correct verbiage, for schema override in file 30_ubuntu-mate.gschema.override, line 6: enable-hidpi='on' and I also change onboard from auto to = true as well under the Arctica section for good measure. Then run the command to update the schema as Ironfoot states in #5.

For anyone seeing later, the Github comment in comment #6 by Sai has been closed as "works as intended." I could not run dfcon-editor as lightdm user using several command methods so I had to revert back to the schema override per #5.