Vibratie

Check if Vibrate is on in the alert sound settings in Settings, System, Sounds. Check if Do Not Disturb is active. 

Check after every step if vibrate works, by setting a countdown timer (for 15 seconds or so), if the watch vibrates when the timer runs out. If it does not: 

Check if power management settings are correct: https://www8.garmin.com/manuals/webhelp/fenix66s6xpro/EN-US/GUID-A4E00381-0673-41A0-8353-67809793E449.html (low power mode may affect if the vibrate works or not)

If that  does not work try switching the device off and on: https://www8.garmin.com/manuals/webhelp/fenix66s6xpro/EN-US/GUID-626CD309-6FCC-4960-81DE-382682FFEC60.html 

If it still does not work: reset to defaults: https://www8.garmin.com/manuals/webhelp/fenix66s6xpro/EN-US/GUID-46551446-AAE7-451C-B857-7D86AD7747EE.html

If all of this does not help, contact Garmin Support.