Block all downloads from SharePoint site - Virtual Data Room

Apologies if there is already a thread to accomplish what I am trying to accomplish.

I am trying to set-up a virtual data room using SharePoint. I have created a new site called "Data Room". The purpose of this site is to share documents (PDFs mostly, but a few PPTs) with external individuals that are not associated with the company to allow them to review documents online. To share access to the site, I have been generating Links to share with "Specific people" at the level of the top folder so that the external user has to access the document library through a link sent to their email and cannot forward it to anyone else. I cannot figure out how to block all downloads of this content. Since the site is specifically setup to house this data, I am happy to remove download capability for anyone that access the site, but also cannot figure out how to do so.

Happy to hear any site based or PowerShell solutions. Thanks!