Whether with touchscreen keyboard or external Bluetooth keyboard, it is possible to select some alternative keyboard layouts. But is it possible to remap keys arbitrarily so as to support various layouts that are not supported in iOS out of the box? If not, are there any workarounds like by installing third party keyboards such as gBoard?
If not, would it not theoretically be possible to develop a third party installable keyboard for iOS or iPadOS which allows one to define custom input layouts? And would it be possible to extend this mapping to support external Bluetooth accessory type hardware keyboards?