Hi
This is a great question. I guess the best initial statement is, there isn't one.
You can create solutions to verify that someone typed a string then added a space and then a string
but that's all you can really guarantee
Then you have the situation where someone types their full name
My name has 4 parts to it.. which wouldn't necessarily work in your situation of how you worded it.
1) are you allowing people to type their full name, or just string space string (first last)?
Firstly I would look here please
These are functions that allow you to add Regular expressions that it tests again. AKA, string space string for instance
Another super simple test is this
I have a text input called FirstLast (yes I am a genius lol)
I have a button.
In the button display mode I have
If(CountRows(Filter(Split(FirstLast.Text, " "), !IsBlank(Value))) >= 2, DisplayMode.Edit, DisplayMode.Disabled)
The reason it is like this is to stop the Blank (space) from being included in the initial steps, this to me is
a bug in the platform side, but the above code ensures that it is only checking is value strings are there
and that there are at least 2 valid ones with a space in between
Picture one I just have the word First
Picture 2 I added the space
Picture 3 I typed their last name and bingo I can save