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Sorry, there is no keyboard shortcut that works (at least on Monterey beta).

But the best way I have is to make them go away quickly, and automatically.

Step 1. Change alert to banner

In System Preferences > Notifications & Focus, change for every app that send irritating alerts, which needs explicit dismiss action.

Change the style to Banners, which will auto dismiss after a few seconds.

Step 2. Dismiss banner quickly

There is a default number of seconds before a banner dismiss itself.

Make it go away quicker. I give 2 seconds of my precious attention.

defaults write com.apple.notificationcenterui bannerTime 2

Run the above command on your terminal.