Hi @Yemata :
I guess the reason you encountered this problem may be:
The list save time as UTC time by default.
PowerApps load time as local time by default.
So when PowerApps load time, it will transfer to local time zone automatically.
In order to solve the problems mentioned above, I suggest you save local time to SPlist and load time in PowerApps as local time too. //make time zone the same.
I’v made a similar test for your reference:
Step1:Set the Default of the Date DATA CARD (not the Default on the Date picker) to
DateAdd(ThisItem.Date,TimeZoneOffset(),Minutes)
Step2:Make sure the Date time zone properties of the date picker control is “Local”

Step3(If you want to update the date):Set the Update of the Date DATA CARD (not the Default Date on the Date picker) to
DateAdd(DateValue10.SelectedDate,-TimeZoneOffset(),Minutes)

Best Regards,
Bof