This monitor is also an Android based large tablet. It is running on an old Android OS which does not support most apps these days. Is there a way to upgrade this OS or am I SOL?
Honestly, any ROM you might find that will run on that device is not going to be new enough to be worthwhile spending the effort to get installed. You'll need a ROM at least 3 versions newer to have the base level of support for apps installing from the Play Store (or to even use the Play Store).