How do you turn off the “Try the new Safari” notification?

I couldn't respond to any comments that ask this question - but posting a solution here as many have asked for it and it seems Apple deliberately avoiding providing a good solution as evident

here: https://discussions.apple.com/thread/252412228

and here: https://discussions.apple.com/thread/252489589

The nagging message can be disabled by applying some defaults using your terminal.app:

defaults write com.apple.coreservices.uiagent CSUIHasSafariBeenLaunched -bool YES
defaults write com.apple.coreservices.uiagent CSUILastOSVersionWhereSafariRecommendationWasMade -float 99.0
defaults write com.apple.coreservices.uiagent CSUIRecommendSafariNextNotificationDate -date "2050-01-01 00:00:00 +0000"

First line tells OS that you've already opened safari

Second line - that recommendation was made in OS version 99.0

Third line says - that the next time it should suggest for you to try safari in year 2050

Enjoy.