Where do shared libraries disappear too?

Turkmick Shared libraries are actually SharePoint sites, so would appear at https://<tenancyname>.sharepoint.com/sites/sitename and it shows you the URL when creating the library. It won't have updated the "Shared libraries" list within OneDrive as the list at the side of OneDrive is just "frequently accessed libraries" so it won't appear in there yet.

Edit: If you put OneDrive into classic mode you might be able to see it, click "Return to classic OneDrive" and then look under "Groups" - here my shared library is called "Test test":

If it doesn't appear in there, and you can't work out what the URL should be then somebody with admin access to SharePoint will need to look in the SharePoint admin centre for it:

• Go to https://admin.microsoft.com/ and sign in with your admin credentials
• Click on "Show all" at the bottom left, then "SharePoint" admin centre
• If it's showing the old/classic view, switch it to the new view (it will tell you this near the right hand side if it's in the old view)
• Click on Sites, then Active Sites
• Look for your site in the list and it will show you the URL, so in the example below it'd be "/sites/Testtest". The start of the URL is your tenancy name then ".sharepoint.com", shown in the "Communication Site" at the top of the list.
  

   

• Bookmark the URL somewhere so you can get back in to the library. It should eventually appear in OneDrive's list once you've used it enough. (There doesn't seem to be a proper definition anywhere of exactly how shared libraries get on that list besides "frequently accessed").