It is still available on ArchiCAD 11 & 12. Look at Work Environment > Shortcut Schemes > Keyboard Shortcuts > List: All commands by theme > 11 Actions > Cursor Snap Variants. You will need to assign "Q" (or any other keyboard shortcut) and Redefine your Shortcut Scheme to permanently apply the change.
While I agree I can add the Q keyboard shortcut I maybe didn't make it clear enough that the actual functionality of being able to choose which variant of projection method is not there in AC 11 or 12 where it is available in AC 10 and earlier.
AC10 the variants are active while I have locked the angle
In AC11 they are greyed out and neither clicking on the icons or using the keyboard shortcut will allow me to change the mouse projection mode.
Also note that with AC11 I wasn't able to simulate the same effect with AC11's Auto Guidelines that I can using the Projection Mode in AC10 and earlier. Seems like we are regressing here rather than progressing
AC versions 3.41 to 25 (UKI Full 5005). Using AC25 5005 UKI FULL Mac OSX 10.15.7 (19G2021) Mac Pro-2013 32gbRam AMD FirePro D500 3072 MB graphics
Works here (both ArchiCAD 11 & 12). The constraints become available after holding the Shift key; or otherwise if using a Guideline or not, hitting Option-a (to lock to the angle), the constraints appear grayed out, but will activate by hitting the "Q" key.