There seems to be some confusion as to what the setting "Open folders in tabs instead of new windows" does (it confused me too). It only opens folders in tabs when you Command double-click a folder within an open Finder window.
If you open a folder by the methods shown above they will still open in new windows (not tabs) no matter what you have "Open folders in tabs instead of new windows" set at.
Change how folders open in the Finder on Mac – Apple Support (UK).
I think you must have the following setting on as well?
Settings > Dock > Prefer tabs when opening documents set to Always .
It seems the combination of the two settings causes the behaviour you are getting.
macos - Force Finder to use only a single window? - Ask Different.
To get around this and solve your problem (without changing your settings), in Finder when there are tabs showing there is a menu item Window>Move Tab to New Window.
The below seems to work and opens the two windows side by side, no matter what tab settings are on. (The pause seems to be needed too.)
Open Two Finder Windows Side by Side (to overide all Tab Settings).kmmacros (8.2 KB)
