How to make ⌘N open a new window in Safari?
Solution 1:
In System Preferences > Dock if Prefer tabs when opening documents: is set to Always that will cause a tab to open instead of a new window.
Changing it to Manually will allow ⌘N to open in a new window.
There is also an In Full Screen Only option.
Solution 2:
Basically user3439894s answer but on macOS BigSur, the option is located in System Preferences -> General menu.