did you install VMware tools on your Mint linux?
if no tools installed, then the "Cmd+Control" is the only way to ungrab Mouse and keyboard.
please go to settings >> keyboard&mouse pane >> doulbe click your profile >>Fusion Shortcuts tab >> first shortcut.
BTW, this shortcut can not be modified from UI.
AFAIK, there is no way to change it.
I guess you don't want all keystrokes are sent to VM, right?