I cannot stress it enough.

Seriously  DO NOT!

A bit of going back in time. Remember the days of Windows 7 or 8 where you had in Windows Explorer a nice group of Favorites for your quick access ?  Most of the people using SharePoint ( and I mean here users not administrators)  would add the document libraries for sync and quick access to that collection.

But the issue that presented itself was: how to distinct between Documents (from site A)  and Documents (from site B) ? Back then the answer was simple: just rename the favorite.

Now, the things have changed in a way that's probably not that obvious to the user.

The Quick Access feature  has two operating modes that merge into a list of locations for quick access:

Mode 1: aggregates a list of frequently accessed folders and puts them in the list

Mode 2: you can decide on "Pinning/Unpinning Items" to the Quick access list

In the above scenario, say you have Documents from Site A and Documents From Site B pinned and you want to differentiate them by renaming them.

Go back to the CAPS : DO NOT!

The reason behind it is that you will be renaming the item itself not the reference to it (in this case the document library in SharePoint, but the same applies to the folders).

Now if you have a little bit of experience, you know what happens when a network share is renamed. In the SharePoint world the implications are more dramatic and even devastating in the Modern Group Sites.

The reason for it is some of the document libraries names are internally bound to the modern group / or site so renaming the Documents Library will result in an error when you try to access the Group Files from Outlook. Of course the document library will continue to work (when accessed from SharePoint) but other components external to SharePoint in the Office 365 space will fail.

Among those, Outlook, Teams,Planner etc.

Not to mention that if you do have permissions and rename a document library in SharePoint, it will probably break the other user's link to it.