I am doing a similar thing based on the input on a drop down menu, you could refactor this for your purposes.
If("Some Text" in DataCardValue2.Selected.Value,true,false)
The above will return true if the condition is met, and false if not. Resulting in a conditionally required field.
So if you wanted to ensure a field was not empty for example, you could do something like:
If(DataCardValue3.Text = "",true,false)
This will return required true if there is no text in the field.
You can also base this stuff on various style properties, here's an example of checking if the field has a red border:
If(TextInput1.BorderColor = RGBA(255,0,0,1),true,false)