Hi @Fulton, Tim ,
Did you create a new SharePoint document library before creating Teams?
I did a test in my environment and it looks normal in Teams client.
1.Add document library in Teams site clicking “Add a tab”, then select “Document Library”

2.Copy the document library link and paste it to “Use a sharepoint link”.

3.We can create a new excel file and open the file normally in it.

If I misunderstand your requirements, please figure it out. Thanks for your understanding!
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