I just tried some tests from my side, and it seems the date string submitted from PowerApps won't change its format in the way configured within the Date column from WorkSheet.
The Date string format submitted by PowerApps would stay in custom format (m/d/yyyy h:mm). And currnetly it seems there is no way to auto-convert the date format submitted by PowerApps within WorkSheet.
Formatting the date string within PowerApps won't help here.
I will collect this from my side.
You may consider to add a code to auto-format the date column within the WorkSheet, when there is new data entered.