> You could also DM an offline friend a tracking pixel to reconstruct their activity, a lot of this endpoint security is entirely up to the user.

Only for as long as they have the steam chat window open and your tracking pixel/message is a recent enough message to be actually loaded. I don't use steam chat enough to remember if they do any of these, but your plan also ignores any possible automatic security/scanning/proxy shenanigans on steams part that will muddy your pixels tracking data or just break it.

    > That logic is acceptable. 

I completely disagree. I use invisible status all the time on steam. I very much have an expectation that when set to invisible my friends would not be able to track my online status.