you probably should start with O365 Information protection policies e.g. Enable sensitivity labels for Office files in SharePoint and OneDrive. Shortly you may configure and apply so called sensitivity labels to files which add additional protection level. Here are few related articles about them:
SharePoint Site to upload and dump files securely ?

Can someone here please share and let me know how and which Share Point Online site to deploy for uploading and dumping files securely for the collaborative tasks?
PCI-DSS and GDPR related files must be secured properly, hence I need some suggestions.
Thanks,
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Emily Du-MSFT 29,596 Reputation points Microsoft Vendor
2022-04-13T06:09:32.187+00:00 Agree with sadomovalex.
You could refer above articles to enable sensitivity labels for Sharepoint sites.
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