To determine if the problem is the device or the operating system you should try on Android, if your tablet is dualboot.|
If the brightness in the other system is also low we may think that the problem is the device.
If, on the contrary, in Android shines correctly, you should go to Windows, options, screen and there determine the level of brightness. If you have activated the automatic brightness according to the ambient light, turn it off.
Try this and if you do not have results comment it to look for other possible solutions.
You have a good day