You're able to select multiple text fields inside the gamerules menu in world creation screen.
This is only visual.
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How to reproduce
Navigate inside the gamerules menu in world creation screen.
Select multiple text fields.
Expected result
Multiple text fields wouldn't be able to get selected/highlighted at the same time, only one at a time.
Observed result
Notice how text fields remain highlighted after clicking more than one of them.
Confirmed. It appears that MC-147605 wasn't fully fixed for all menus as this problem can still indeed be seen within the gamerules menu. With that being said, this report relates to MC-147605.