Thanks for getting back to me on this @timl , I was about to abandon the notion of a solution - at least for a season until MS come up with a workable solution. I'll give everyone a heads up here, in my labours to test your previous options I have uncovered another error that is related, but have reported elsewhere (I had been advised by another super user not overload each query with multiple questions and asks. That said, if it will help anyone reading this understand better about the scope of my endeavours, a link is here. ) Now back to answer your questions...
@timl wrote:
Hi @Anonymous
Thanks for clarifying that.
When loading a record, formula beneath will format the value as a percentage if the underlying value is a number. Otherwise, it will set it to the text value.
If(
IsNumeric(Parent.Default)
Text(
Value(Parent.Default) * 100,
"#%"
),
Value(Parent.Default)
)
If you still want it to display "not applicable" when blank, the formula would look like this.
If(
IsBlank(Parent.Default),
"Not Applicable",
IsNumeric(Parent.Default)
Text(
Value(Parent.Default) * 100,
"#%"
),
Value(Parent.Default)
)
With regards to the text input control not accepting a number, can you confirm the format property of the control? Is it set the 'Text'?

The control I have used the above control "Percentage_Test" for test purposes only. I set it to Single line text on SP.
Another issue I have discovered. When I changed the columns (scoped to accept text and %) from Number to Single line Text, while there was no loss of data incurred (something SP warns you against), I lose the %. For eg 78% now appears as 0.77.
It seems to me then, please correct me if I am wrong, that what you gain on the app by offering the option to enter data as text or %, you lose it at the SP end.