what does it mean when the plug symbol appears on my battery for my macbook air

Connected to power but not charging.

For more info: If your Mac battery status is “Not Charging”

Startup in Safe Mode. https://support.apple.com/guide/mac-help/start-up-your-mac-in-safe-mode-mh21245/mac.  

    Quote:

    It also does a basic check of your startup disk, similar to using First Aid in Disk Utility. 

    And it deletes some system caches, including font caches and 

    the kernel cache, which are automatically created again as needed.