I want to export my dataset to excel, but only a subset of variables. When I go to File > Export... > Excel, it immediately goes to where I want to save the file and doesn't bring up the export dialogue to allow me to select which variables i want to export.

I'm running SPSS 26.0 (I think) on a Mac (v. 10.15.6 - Catalina)

When you go to that link, you should see a Variables button that will let you select the variables. However, if you are actually on V27 on a Mac, it uses native Mac file dialogs by default. In Edit > Options you can turn off that behavior, and then you should see the full functionality including variable selection.

That did it! Thank you.