Prior to getting Premium, YouTube was able to detect that I was watching a video (and nag me about premium as a way to get rid of ads). Since getting Premium, I haven't gotten the nag message.

I run AdGuard (on a Mac). It has a filter log feature.

Poking at the log while playing a video, I do see calls to ttps://{{clusterid?}}.googlevideo.com/videoplayback?expire=1758173247&...

However, this call is not being blocked.

I suspect that this is the "keep watching" feature that tracks where I am in various videos (switching from one logged in device to another keeps the same position). Watching the video all the way through, I don't see any requests relating to this getting blocked while on Premium. This feature is also likely more than sufficient data to attribute a view (and monetization of the view).

There was also a call to ttps://www.youtube.com/youtubei/v1/log_event?alt=json that was not blocked.

I do see some doubleclick.net links being blocked, thought that could be from any number of other pages I've got open.

Going to an incognito session and pulling up the same video (Once Around Trappist 1)...

There's now a call (that has gotten blocked) to ttps://www.youtube.com/api/stats/watchtime...

That call was not something that I saw when logged into premium. This rule is described as "@@||www.youtube.com^$generichide (AdGuard Base filter)"