The toolbar that appears in a document library (or list) in SharePoint Online can be customized (to an extent). We can hide, rename, change icons, and even rearrange the commands.
Here is an example of a default library. By default, we see commands to create documents, Upload, Edit in Grid View, Sync, Add shortcuts to OneDrive, Pin to Quick Access, Export to Excel, and many more below the sub-menu.
Here is an example of the library toolbar that has nearly everything hidden.