Universal Control is perhaps one of the biggest updates, allowing a single mouse, trackpad, and keyboard to be used across multiple Macs and also the iPad for moving content between devices. There's also a new AirPlay to Mac option for AirPlaying movies, games, photos, and more from the iPhone or iPad to the Mac, plus the Mac can be used as a speaker for multiroom audio. https://cluttons.co.za/
Safari has an optional new tab bar design that better blends into the background and Tab Groups for grouping your open tabs together to make it easy to swap between different tasks without having to lose your open tabs. Tab Groups sync across all of your devices and can be shared.