I had to re-install the Super Collection and the game has decided to start in Windowed mode for some reason. I ticked the option box for "fullScreen Mode" but to no avail..it only seems to be in this windowed mode..which is bad, because no scrolling plus the Dock items show.

I have re-installed twice this evening to fix various problems and this has begun with these re-installs.

How the heck to force my game to be Full Screen again, as it was for the past few months?

I'm really puzzled by all the bugs I am encountering tonight after months of no issues.

I hope someone can help...I am having so many problems tonight.

I don't how it works on Mac but I believe if you press on ALT+Enter, it will switch from windowed mode to full-screen mode and vice-versa. But maybe, this only works for Windows.

You should delete the Preference file and see if that helps.

delete the pref file for The Sims 2. It has this name: com.aspyr.sims2.appstore.plist

There are two copies of the file.
Look here in this path: ~/Library/Preferences
And Look here in this path: ~Library/Containers/com.aspyr.sims2.appstore/Data/Library/Preferences
Note that ~ stands for a Folder inside the User Folder, or your Home Folder…Same thing.

Easy way to look is copy the path I give you, start from ~ and copy to the end, then in the Finder look in Go menu then "Go to Folder" menu.

Using Go To Folder is by the easiest way to find some of this stuff.

if not then reinstall go to the App Store and download the latest version.

First: Make a back up your The Sims 2 folder.
Located here: ~/Library/Containers/com.aspyr.sims2.appstore/Data/Library/Application Support/Aspyr

Note that ~ stands for a Folder inside the User Folder, or your Home Folder…Same thing.