Warning: This deletes everything. Only do this if you have a backup.
There is no single "refresh" key for the desktop. Instead, use: how to refresh on a macbook pro
If a restart didn’t fix the lag, your SSD is likely cluttered. Here is how to clean house. Warning: This deletes everything
In that same menu, turn on:
If your MacBook Pro is feeling slow, "refreshing" your system by clearing temporary cache files can free up space and improve speed. How To Clear The System Cache On A Mac how to refresh on a macbook pro
: This is the most effective way to "refresh" the desktop environment.