Here are some things that existed for a long time but still blow my mind (note: this is not "modern macOS", I migrated to Linux long time ago, so forgive me ignoring modern flaws).

- The preview app - document editing at its best

- Apple Mail Search - you can filter by nearly every aspect, even between dates

- the mighty Alt key (alt+click unlocks an extra feature all the time, alt + shift + volume makes smaller steps, etc)

- apple headphone remotes also work on macbooks

- you can turn off the display by setting 0 brightness

- Printing just works - everywhere

- the trackpad integration

- brew is just awesome