FCC filings for the S Pen Pro, a bigger version of the S Pen with Bluetooth, have been made public, and reveal that the upcoming stylus will support the unannounced Galaxy Z Fold 3.
Samsung Galaxy Z Fold 3 durability: Did the phone stand up to 18 hours of S Pen use? - CNET
Samsung Galaxy Z Fold 3 announced with S Pen support and water resistance - The Verge
Samsung Galaxy Z Fold 3 S-Pen Pro compatibility hinted by FCC
F-TECH Fold 3 S Pen Fold Edition Stylus Pen 4096 Pressure Replacement for Samsung Galaxy Z Fold 3 5G Touch Screen Stylus S Pen with Tips (Black) : Cell Phones & Accessories
Does the Samsung Galaxy Z Fold 3 support the S Pen?
Samsung Galaxy Z Fold 3 announced with S Pen support and water resistance - The Verge
Samsung Galaxy Z Fold 3 will support S Pen Pro, FCC reveals
Samsung patents an interesting way to house the S-Pen in a dual-folding device - PhoneArena
Samsung Galaxy Z Fold 3 announced with S Pen support and water resistance - The Verge
Can confirm, the new slim S-pen for the Fold 5 works on the Fold 3 : r/GalaxyFold
Galaxy Z Fold 3 hands-on: Built stronger for durability and S Pen support