Android
Manage Keyboards on Android auf Android
Android ships with Gboard as the default keyboard, but any keyboard app installed from the Play Store stays inactive until you turn it on manually. This works as a safety measure, since an unapproved input method could in theory log every keystroke, so Android forces you to enable it explicitly under Languages & Inputs.
If a newly installed keyboard app does not appear when you tap the keyboard switch icon, the toggle in the on-screen keyboard list was likely never flipped on. The same setting also lets you turn off keyboards you no longer use, which shortens the switch menu and keeps it easier to scan.
Where to activate a keyboard
Go to Tap on Settings ➔ Tap on System ➔ Tap on Keyboard ➔ Tap on On-screen keyboard. Every installed keyboard app appears in this list. Tap the keyboard you want, flip its switch on or off, and confirm with Tap on OK if a data access warning shows up.
Turning off a keyboard here does not uninstall the app, it only removes it from the switch menu. You can reactivate it anytime through the same path. If a keyboard still does not appear after activation, check whether the app requires an extra permission grant on its own settings screen.