Hi
In fact, Keyboard overlay issue can be easily overcome by sliding the screen and then you will be able to see what is underneath.
However, this is NOT soemthing users want. (Not user friendly).
If you look at PowerApps sign-in page itself, it already showed that PowerApps user sign-in and password sign-in also having keyboard overlaying on the input box. I DON'T WHY PowerApps team has not mentioned or improved this from DAY 1 until 343 days.
Meantime, the keyboard overlay issues (in my case), happened 50:50.
I am using (as well as my customers) highlighted to me that sometimes the input area will move up automatically when keyboard is pop-out but not all the time.
I wish PA can look into this even from the time you sign in to PowerApps.
(On all devices)