As of the 2019.1 release, Mudbox automatically resized its interface to match the resolution of your monitor. If you have a high DPI monitor, such as 4K, the Mudbox interface rescales to twice the size. For high-resolution monitors, this may lead to less sharp text and icons in the user interface.
You can disable the automatic interface scaling to return Mudbox to its original size. If you do this, Mudbox reverts to the original 1:1 scaling, and text and icons are sharper but smaller overall.
To disable automatic interface scaling, append the flag -noupscale to the Mudbox.exe string each time you want to turn off the automatic scaling: mudbox.exe -noupscale.