I want to add a pie menu item (from Shift+S menu, Cursor to Selected) to Quick Favorites (the menu that opens on Q), but I only know how to add to favorites through right-click, which does not function inside the pie menu. Any other way to add an item to favorites?
You might don't know where you can find the function in menus, or even if it can be found in the interface. But everything in Blender you can find using quick search, Just press F3 and type what you want:
As you see, it is tolerant to mistakes.
Once you've found the operator, you can use right click to add it to quick favorites: