Based on my recollection when discussing support for third-party keyboards on iOS Apple seems to go out of their way to mention that sensitive information/keystrokes can be transmitted to the keyboard developer.
Are such fears overblown or is there a way to disable transmission of such data to the keyboard devs?
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I see no reason to switch from the default iOS keyboard but am curious nonetheless should I want to try out third-party keyboards in the future.
There is a checkbox when installing that asks if you want to give the developer access or not so I assume no access is given outside of the offline app unless you check this box.