Since the release of OpenCore since 0.7.6 the UIScale key can be found in the UEFI
section in the Sample.plist. Default for this entry is '0'.
View attachment 564651
In older versions of OpenCore 0.7.5 and earlier, there was a NVRAM UIScale entry, as shown below from the Sample.plist from OC 0.6.9
> Data > <01
View attachment 564652
If I recall correctly, ocvalidate generates an error when both UIScale keys/entries are present in the config.plist. So adding a NVRAM UIScale entry may not work.
You probably need to use the current UEFI > Output entry, change this number to '2' to see if it makes any difference.