Starting with the October 8th 2025 5.18 Android release, notifications sent from phone to watch no longer vibrate the watch.
I wear a Garmin Forerunner 255 and use a Google Pixel 9A with the latest version of Android as well as the most up to date security release.
If I set a timer or alarm on the watch, it will vibrate at the conclusion of said timer/alarm, but all notifications received on the phone sent to the watch simply do not vibrate it.
It is not related to “do not disturb”, that setting is turned off.
I downgraded to the 5.17.2 and the watch started to vibrate on phone notifications again. Therefore, as far as I can tell it is a software bug with Garmin Connect version 5.18.