Samsung just released the Galaxy Z Fold 4 as well as an S Pen case to go with it that solves the problem of stylus storage.
My solution for s pen and stand on galaxy z fold 4. : r/GalaxyFold
Galaxy Z Fold 5 Case With S Pen Holder – Poetic Cases
Galaxy Z Fold 4 fixes the S Pen case problem
samsung Galaxy Z Fold 4 5g Flip Case With Stand & Pen Slot
Galaxy Z Fold 4 to have S Pen storage, report claims - 9to5Google
Temp fix for Fold5 S-pen cases : r/GalaxyFold
Galaxy Z Fold5 Slim S-pen™ Case, Sand Mobile Accessories - EF
Galaxy Z Fold 3's S Pen case doesn't match Note's legacy - 9to5Google
Samsung Galaxy Z Fold 5 problems and how to fix them - Android
My solution for s pen and stand on galaxy z fold 4. : r/GalaxyFold