@JohnnyEnzyme@lemm.ee isn't part of the point of ActivityPub to avoid vendor lockin/single point of billionaire enshittification? I read and interact with a fair amount of Lemmy content through an Mbin instance.
You can already limit Google using site:[DOMAIN].
If every ActivityPub driven service used a common TLD like .edus, you'd be able to limit results to that facet of Google's index, they don't. If they did, we'd be back to a single point of failure.
Google supports limiting searches to content using a Creative Commons license based on the licensing metadata in the URL. ActivityPub content already has the metadata, but it took a decade to generate enough content before Google offered the option to filter searches by CC-BY-SA... and Google was a VERY different company back then.