When I select the water level manually, it is set to water level 7 by default.
Did you press the Water Level button right after pressing the Power button?
Fully automatic washing machines set the water level automatically by detecting the load of clothes [weight of the laundry] during the washing operation.
When you press the Power button and then press the Water Level button, water level 7 will be set by default without the machine detecting the load [weight of the laundry].
This is an operation method designed to prevent damage to the laundry as there is a possibility of damage to the laundry when the washboard spins during the wash cycle if the water level is low compared to that required by the laundry load.
Try this
If you wish to change the water level, you can press the Water Level button additionally to set the desired water level.
This guide was created for all models, so the images or content may be different from your product.