Out of the box a SharePoint Online Document Library displays what is known as simple controls just below the Document Library name as highlighted above. These button are typically new, upload, sync, edit, manage and share.
However, you may see a situation where they are no longer displayed as shown above.
If you want them back, here’s what you need to do.
The reason they are no displaying is because the current view of the document library is not based on the default view style.
You’ll need the rights to change the Document Library, but if you can select the Library tab at the top of the page to reveal the Ribbon Menu.
On the Ribbon Menu locate the Manage Views section, on the left hand side. Then select Modify View as shown above.
Scroll down to the bottom of the page that is displayed and open the Style option.
As you can see above, the current style is set to Shaded.
Change this to Default and Save the changes.
You should once again see the simple controls as shown above. Unfortunately, you may also lose some of the functionality that you desired with the previous style. At this point in time you can have one or the other option but not both.