Hello ilyafar,
Thank you for reaching out to Apple Support Communities, and we'll be happy to help in any way we can. We understand you're having issues with video lagging when using the Touch Bar to adjust the brightness on your Mac. First, test this issue in another user account. To do that, log out of your current user. Then, log back in under another Standard or Administrator account and see if the same issue occurs there. This way we can tell if it is an issue with your user account, or if it is system wide: Set up users, guests, and groups on Mac
If it occurs in another user, let's test this issue in safe mode. Safe mode (sometimes called safe boot) is a way to start up your Mac so that it performs certain checks on the software: Start up your Mac in safe mode
Let us know if the issue persists in safe mode, and we'll move forward from there.
Cheers!