In SharePoint Online Modern Experience, As we navigate into folders and sub folders, it adds link to the parent folder in Breadcrumb above List/Library View.
I have created 4 Level subfolders in document library.
While in Classic experience, we get the link of parent (only 1 level).
I can think of options, both of them would require you to write code.
Option 1 - Use jquery, and find the main div element which is rending top link bar. Further write logic to find all the links and its title from the dive element and create your custom html. add your custom html to left navigation container div. Hide top link bar main container div using ...