As far as we're aware, the fold 7 lacks the chips in the display to support spens. Nothing you can buy can add support back. As johnz said, they will be scams trying to get money from people looking to add spen support.
Spens technically use the exact same technology as wacom drawing tablets. Most of the system is in the screen, not the pen. So the screen not having the technology in it means there's no way to make it work if it never came with it.