This is a bug: https://bugs.chromium.org/p/chromium/issues/detail?id=1264148#c30

There is this reddit thread that suggests a workaround:

https://www.reddit.com/r/MacOS/comments/qibzpx/huge_gap_at_the_top_when_chrome_is_in_fullscreen/**strong text**

solution 1: full screen chrome --> gap shows up --> three finger swipe up --> three finger swipe down --> gap disappears.

solution 2: Found temporary fix System Preferences --> Dock & Menu Bar --> Make sure "Automatic Hide and Show Menu Bar on Fullscreen" is checked

This is a bug: Issue 1264148: Empty space above tab bar in Monterey with Menu bar when "Automatically show and hide the menu bar in full screen" is disabled.

There is this a Reddit thread that suggests a workaround: Huge gap at the top when Chrome is in fullscreen

• Solution 1:

  full screen chrome --> gap shows up --> three finger swipe up --> three finger swipe down --> gap disappears.

• Solution 2:

  Found temporary fix System Preferences --> Dock & Menu Bar --> Make sure "Automatic Hide and Show Menu Bar on Fullscreen" is checked