The brightness you set on your monitor's HUD or with some dial on the monitor doesn't affect video you record. It's some internal adjustment just within the monitor. So you don't need to care for this kind of brightness adjustment.
You don't see this locally, because if you play back your naturally bright video, it will get brightened up by your monitor, so you don't see a difference between the original and the recording. Actually, this is proof the added/reduced brightness isn't in your video, because if you would record the brightness of the monitor as well, playing back would be double/half the brightness - increased/decreased twice: once by the original, twice by the playback.
However, you should try to run your own monitor with about the same level of brightness most people run their monitors, so you will see what they will see. Using filters to adjust brightness on your video is the wrong approach. This is a guess how bright your users might have locally, but this is almost always a wrong guess.
Brightness isn't that important by the way, it's contrast. If you adjust brightness, you should also adjust contrast. Whatever you set the brightness, it's the contrast you need to adjust afterwards to make sure you still see a difference with the brightest parts and a difference on the darkest parts of an image.
A rule of thumb is that you actually adjust the darkness level with the brightness slider and you set the actual brightness with the contrast slider. To reduce the "brightness", reduce the perceived brightness with the contrast slider. Black parts will become dark grey. Now tune down the brightness to make this dark grey almost black again. Now increase the brightness a little bit to both get your white to your desired brightness level as well as make the darkest grey parts black again.
All this isn't reflected in any video you capture. These are always how the apps created it in the first place. You only have to make sure you don't adjust brightness in your video driver control center - this could definitely distort the colors in your video. If you have a Nvidia GPU, this would be the "Adjust desktop color settings" section of the Nivida control panel - just make sure you don't adjust anything here but use the defaults everywhere.
