Is there a keyboard shortcut to lock my Mac mini?
Launch System Preferences and go to the Keyboard pane.

Next, select the “Keyboard Shortcuts” tab. From the list on the left, select “Application Shortcuts”. Click on the plus (+) button below to add your new shortcut.

In the dialog box, we’ll want to leave “All Applications” selected in the first menu. Enter “Lock Screen” as the Menu Title. Finally, enter your keyboard shortcut. Let’s go with Command+Shift+L.

Click Add and you’re all done!



You also can explore https://support.apple.com/en-us/HT201236 for the official Apple shortcut.