I think there are work arounds for it. How do you use teams in the browser or in a app? First of all i think it should be possible to send more files at once. But what you could do is prepare a share and share the link with the people on the call so they have the documents directly.
If you mean sharing a document on screen, you can certainly switch between multiple documents within a given application (say Word), or alternatively, you can share the entire screen and any and all applications/documents currently opened on it.