Explanation/Reference:
Explanation:
Viewers must be prevented from printing documents that are stored in a modern site named Finance.
Restrict Print:
1. Firstly, we need to activate Rights Management from Office 365 Admin center. Go to Admin Center > Settings > Services & Add-ins > Microsoft Azure Information Protection.IRM - Information Rights Management is applied to files at the list or library level. IRM feature requires an Office 365 E3 subscription.

2. Go to Site/Subsite > Document Library > Library Settings.

3. In Library settings, go to Information Rights Management.
4. Click Restrict permissions on this library, provide the name & description.

5. In below image you can see, how the print option got disabled after enabling IRM for document library.

References:
https://www.cloudfronts.com/restrict-download-and-print-option-for-sharepoint-online-document-library/