Also, since you are on MacOS, you can bind a keyboard shortcut to the 'Enter Full Screen' View Menu item.
Open MacOS System Preferences
> Keyboard
> Shortcuts tab
> App Shortcuts
Click the +
Under Application, select Photo Mechanic 5
Under Menu title, type the following:
Enter Full Screen
Then pick a keyboard shortcut. I think Shift-Command-f is safe to use, but if thats taken, select your own. Once you do this, you can use that keyboard shortcut to pull the Preview Window into a full screen mode. Note, Esc will still close the Preview window. If you want to bind a keyboard shortcut to "Exit Full Screen" you'll have to do that separately.
Having the option to always open Preview window in a full screen mode could be useful. I encourage you to add the request in the Feature Request area of the forum, but be aware that it won't be addressed until after our next version. :-)
Thanks,
Mick