Thanks...Almost there...
Clearly the % pull-down and the GPU checkboxes should all be changeable - so something is wrong with the way the MAC is interpreting their 'disabled' status
It's not so clear from your image - can you test this please...
If you click the left-hand
Resolution checkbox to become
unchecked do all of the options to its right 'gray-out' [=become 'disabled']?
If you click the left-hand
Resolution checkbox to become checked do all of the options to its right become 'enabled' [=text fields are editable]? The % drop-down should be enabled too - but I can see that it isn't on your MAC ?? I also see that the other pull-downs look disabled too - time for some alternatives...
If you click the left-hand main
GPU checkbox to become
unchecked do all of the numbered GPU checkboxes go unchecked and disabled [grayed-out] ?
If you click the left-hand main
GPU checkbox to become checked, then by default checkbox '1' should become auto-checked, BUT thereafter you should be able to change any of the four settings until the main one is unchecked when all four should all become unchecked and disabled...
With other checkboxes - when toggling them on/off does that affect the disabled state of the options to their right ? When a checkbox is unchecked its options to the right
should become 'disabled'/grayed-out [except the two sliders which have proved to be 'non-disable-able' even on a PC!]. When it's [re]checked its options should become 'enabled' again.
Thanks again for the help - I hope we can shortly get all of these MAC niggles resolved... After your reply I'll look at some alternatives to try and fix this final annoyance......