I can't enter text on Samsung Galaxy Z Fold

You are probably using the app when the phone is folded open,. Try closing the phone and using the app on the outer screen.

For more information, see Samsung's support site:

​https://www.samsung.com/in/support/mobile-devices/galaxy-fold-how-to-switch-apps-from-main-to-front-screen-when-folding-the-device/