Dear Daria,
Greetings! Thank you for posting in the Microsoft forum.
When you create a new file or upload an existing file to Files tab in Microsoft Teams, it automatically updates to the associated SharePoint site. Please note, by default Files tab in teams open General folder, please check the General folder in the document library in the site.
Also, try clicking the ellipses on the ribbon (three dots) and select Open in SharePoint, it will open a browser, check if it shows the file.

If the issue persists, please provide us with some related screenshots showing how it appears in Teams app and SharePoint library.
We will look forward to your reply. Stay safe and stay healthy.
Sincerely,
Neha Singh | Microsoft Community Moderator
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