I am not sure what you mean by "all of a sudden" your green screen option is gone.
Premiere Elements 11 and 12 Mac do not offer Chroma Key, Green Screen Key, or Blue Screen Key. These are Windows Only features.
I have suggested that use of the Difference Matte as a replacement. Although Videomerge is available in Premiere Elements Windows and Mac, I do not prefer this choice.
I assumed that this would be the case for Premiere Elements 9 Mac and Premiere Elements 10 Mac? The following online
article supports the Windows Only for the Green Screen Key when it comes to Premiere Elements 9 Mac.
So what is the basis for your statement
Ive made green screen stuff before, but all of a sudden my green screen option is gone!
Where did you do this prior work...on some version of Premiere Elements Windows?
Please explain further.
Last time I used it was on a Windows computer. I just assumed it would have the same options, as it is the same software. I guess I was wrong. Is there any way to still get the green screen effect??
As far as I know, there is no Green Screen Key that you can obtain for Premiere Elements Mac.
If you want to use Premiere Elements Mac for a green screen project, then the usual recommendation is to try to do your green screen work with Videomerge. As I said, Videomerge is not one of my effects of choice.
Many Premiere Elements Mac users seeking to do this green screen work have had success using the Difference Matte as described in my blog post mentioned in the previous post in your thread.
Please review the details and maybe give it a try and let us know if it works for you also.