You need to transcode (convert) video together with chosen video filters.
Adjust Brightness and Contranst the way you already do it in video effects dialog box.
Then Media > Stream... where you include "vfilter=adjust" in your transcoding chain.
https://forum.videolan.org/viewtopic.ph ... 47#p381148
Or enable the "adjust" video filter for transoding in VLC prefererences:
Tools > Preferences > ( Show settings = All ) >
> Stream output \ Sout stream \ Transcode: [v] Image properties filter
Save changes, restart VLC.
Then Media > Convert / Save...