For reliable/consistent synchro­nization with metadata and useful additional features (e.g. email archiving from Outlook to the Share­Point library), you will get a third-party tool.
We could show a demo through system partner­ships if you are inter­ested here.

If deacti­vation is desired, please proceed as follows:

1) You can deactivate synchro­nization at the document library level via library settings:

Sync

Click “Advanced Settings”:

Erw.Einstellung

Choose for “Offline Client Avail­ability”: No

VerfügbarkeitOffline

Then select OK at the bottom of the list.

2) If you want to disable synchro­nization for all libraries in the site, this can be controlled by the site settings:

Select Settings and Site Infor­mation, then View all site settings:

Websiteinformationen
Websiteeinstellungen

In Search section you will find Search and Offline availability:

SucheOfflineVerfügbarkeit

Also, turn off the option to download to Offline clients here:

Herunterladen

3) If you want to avoid syncing with OneDrive in general, go to M365 administration.

Select All admin center and then OneDrive:

AdminCenter
OneDrive

Select the first point (Show the Sync button…):

SyncOneDrive

This setting is set globally and only has an effect after a few hours.