SureAI

So, I love Enderal so much, and to criticise it feels almost cheeky, but I was wondering if it's intended to be as dark as it is for me, or if I'm the only one experiencing it; for example, dungeons are not just a little bit dim, they're totally pitch black, which makes it difficult to play an archer character as to see I need to be carrying a torch at all times. The brightness setting doesn't seem to do anything, so I was wondering if this could just be a problem on my end?

Do you use an ENB? Disable it.
Try to change your monitor settings or your settings in the graphics card driver.

I don't use an ENB, I had some lighting mods installed for Skyrim but I imagine they're totally disabled in Enderal. I'll tweak what I can.

Upon experimenting with some settings, it turns out that somehow onetweak was causing the issue; as soon as I disabled onetweak I could change my brightness settings.

I had the same problem as you, but it isn't Enderal's fault. It has been like this in Skyrim since always, that the brightness regulator has no effect, when the game is run in Window Mode. Only in Full Screen Mode it would do its job, this is how it was in my game at least.
OneTweak forces you to play in Borderless Window Mode, therefore the Brightness isn't adjustable anymore. OneTweak is only indirectly to blame, the real issue is the display mode.


However, it's a shame that i will also have to deactivate OneTweak just to make my game brighter (my monitor already runs at 100% brightness), since it supposedly makes my game crash less with OneTweak activated.