Extensions : application customer include a left-nav placeholder which will allow options to hide, pane or customise
there are many requests for leftnav customisation options which often come in business requirements. Nav is always something that users get quite excited about.
why not combine this with the work being considered on new placeholders for the application customizer
include a simple script way of specifying that you want
no left hav
narrow left nav with icons only (like VS code)
standard left nav but in flyout pane to conserve space(like modern details pane)
fully customised and specified in extension