Signal generates the preview on the sender’s device, which means the sender takes on the privacy burden for fetching data from a message, and my evil server can’t track your device unless I tell you to send me a link from my website

Sable fetch it on the server host, but Sable took the Signal's approach with Matrix Specification Changes (MSC) 4095 bundled URL previews

To test different approach, one strategy is to move "link preview generation into a separate library, which lets us do fun things. We can now make architectural decisions on where we do link previews without doing a ton of refactoring work.