I just create the 2 sharepoint lists.
one for collecting all the leave requests ad one for the leave balance like this.

But I have a problem that, It works only for one user.
I mean on my Leave request app, I want the users to see how many leave balances each type that they have left. like this.

but I don't know how to make it works for all users.
Example
User A
- sick leave balance (maximum) = 10, Annual leave balance (maximum) = 20
- already request the annual leave 4 days ->> current annual leave balance = 20 - 4 =16
User B
- sick leave balance (maximum) = 10, Annual leave balance (maximum) = 20
- already request the sick leave 1days ->> current sick leave balance = 10-1 = 9
I don't know how can I make the sharepoint know that the current annual leave btw User A & User B is different , also how can I update the data for showing on the Power apps.