Basically, below a seemingly-arbitrary threshold (seems to be around 60%) my laptop screen is too dark to really make out much, and above that threshold it takes its maximum brightness (which is waay too bright for my eyes).
This problem only occurs when I change the brightness using Windows' UI. Changing the brightness using Fn keys on my keyboard works as expected; unless the screen went into dark mode because of Windows, in which case they have no effect.
This problem started occuring on my ASUS laptop very recently. My laptop has a poor battery, but I don't think that's related.
What is going on? I tried resetting power plan settings, turning off adaptive brightness and restarting. I'll give any info asked for. Help required urgently...
Update: here's another issue (thankfully, resolved for the moment) related to my screen too: Laptop screen turns off on removing power cord.