Apple shifted from its former shortcut in macOS to the new Control Center.

Disabling notifications in macOS is a great help during meetings, whether you’re sharing your screen or trying to avoid being distracted. In macOS Mojave and earlier, you could Option-click the notifications icon in the upper-right corner of the screen to temporarily shift into Do Not Disturb mode.
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https://www.macworld.com/article/3599131/how-to-turn-on-do-not-disturb-in-macos-big-sur.html