Video wouldn't upload cuz bigger than 10mb
Uploaded to yt instead
idk if its a setting in the shader or not and am very dumb

edit: the first part of video with it working is with shaders set to off
another edit cuz line 3 above: with shaders on it does still effect the minimap tho

Looks like Sildur's shaders don't use Minecraft's brightness slider. You can change the brightness settings of the shader via Video Settings > Shaders > Shader Options > Color.