Additional features, settings, or issues not covered by specific Microsoft Teams categories
Got the same problem and found the solution here: https://www.cloudservus.com/how-to-remove-a-synced-teams-folder-from-windows-file-explorer/
Right-click on your one-drive icon in system tray to open settings. In the "account" tab select to folder you want to stop synching. Afterwards you can delete the folder in your network drive.
BR
Dirk