As a Roblox developer, it is currently impossible to completely disable a TextBox.
I have dynamic forms where some fields can be active or inactive depending on the situation. In case the field is inactive, TextBox should not be able to receive focus.
TextBox.TextEditable prevents typing inside the TextBox, but still accepts cursor focus inside it.
There are some, but incomplete, workarounds, all needing some relatively complex algorithm and several lines of code to achieve this goal.
If Roblox is able to address this issue, it would improve my development experience because this will generate a more consistent form when a TextBox is inactive.