NOTE: If you are unsure how to start syncing files/ folders in OneDrive, there is an article by Microsoft here (although a little out of date).

You can sync libraries, files or folders from SharePoint & Teams in your OneDrive app. The former was released in 2016 and dropped out of support in 2019. Affected are macOS Sierra 10.12 and macOS High Sierra 10.13. Here’s how you stop syncing and remove the contents from your OneDrive app. Microsoft is wielding the axe on the OneDrive sync apps for older versions of macOS and will focus only on the three most recent incarnations from September onwards. In the Storage page, unfold the Advanced storage settings and choose Backup options in the drop-down menu. In the default System tab, scroll down to find the Storage option and click on it. From time to time you may not want to sync these files or folders any longer. Click on the Windows Start icon and select the Settings icon (gear icon). Syncing libraries/ folders or files from SharePoint or Microsoft Teams lets you his lets you work directly in file explorer in Windows, access files even when you’re offline and sync any changes made to files automatically when you’re back online. Choose the location you wish to stop and press stop sync. How to remove the contents from the OneDrive app Click on the OneDrive app icon > under Help & Settings > Press Settings.In this post we will detail how to stop syncing libraries or folders from SharePoint or Teams and then how to remove remaining contents from your OneDrive.

Manage onedrive sync settings