Indoor and evening photos come out dark, and the obvious fix, winding brightness up, usually makes them look washed out instead.
Brightness lifts everything equally, including shadows that are meant to be dark. Push it too far and the picture turns flat and grey rather than bright.
Contrast pushes dark and light apart, which is what makes a picture look properly exposed. A small brightness lift with a larger contrast increase almost always beats brightness alone.
If the photo was taken under yellow indoor light, pulling saturation down slightly often looks better than trying to fix the colour directly.
Raise brightness in steps to somewhere between 120 and 150 percent, then add a little contrast to stop the picture looking flat. Dark photos usually contain more detail than they show, and a modest lift brings it out.
Going much further turns the shadows grey and makes grain and noise stand out, especially in a photo taken in low light. If a picture is very dark, it is better to lift it by a moderate amount and accept that some of it stays in shadow than to push it until it looks washed out.
No. What you see is a preview. The file is only written when you press the button.
No. These are straightforward adjustments, predictable and the same every time.
No.
Beyond about 150 percent the shadows turn grey and noise becomes obvious. Stop earlier and use contrast to give the picture some depth.