Joe hos is Do not disturb related to it all?
In both iOS and MacOS "Do Not Disturb" silences calls and notifications including notifications of calendar events.
Actually, I don't even know what Show Previews > Always achieves, but I trust you so I just mentioned I dont' see Show Previews > Always offered on normal desktop OS.
"Show Previews" is unique to iOS and iPadOS and controls the display of Notifications on a locked screen. Why it is "Show Previews" and not "Show Nofications" you will have to ask the human engineering group at Apple in Cupertino, California but I guess it was intended to prevent confusion.
Not sure how Do not Disturb feature follows up on not being able to find Show Previews > Alway on desktop.
You cannot find Show Previews > always on any MacOS device such as your desktop because it does not exist
per. se. However System Preferences > Notifications > Do Not Disturb provides the same functionality on MacOS that Settings > Notifications > Show Previews does in iOS and iPadOS.