I think I remember him endorsing signal years ago which gave it at big boost at the time

What an awful take on this issue

most likely yes.

My point is, if youtube customizes the feeds based on the IPs, then the youtube accounts used are not really “fresh” but there’s already some data entered into the profiles upon their creation.

fresh YouTube account

change their location to a random city in the US

yeah but you’re still bound to IP addresses. I was under the impression Youtube used those for their profiling