How to Fix a Flickering External Screen on a Mac
If you’re using an Apple display with your MacBook or desktop Mac, things are generally flawless. However, non-Apple displays can exhibit weird behavior such as flickering, and it’s not always obvious how to fix it. There are some things you can try, though.
Adaptive Sync Book Air Displays Selecting Refresh Rate Display Variable Resolution Static Resolution Dropdown Menu
Source: howtogeek.com