I'm not going to say it's not technically possible, because it is (although it would be a huge battery or bandwidth drain, not to mention an insane tech scandal if found to be true); but if the only proof you have is a video feed that resembles your conversations I'm going to guess you're giving that data to Google is some other way. There are a thousand ways this could be happening, and most them have a psychological component.

I've made significant efforts to minimize dependency on google services and these are items that appear w/o any interactions or data being explictly shared to the google platform. It was hard to believe at first, but after quite a bit of testing I realized what was happening.

Have you considered that this traffic is impossible to detect or block because... it doesn't exist?

there's traffic that gets through services like netguard that's calling home to services like mtalk.google.com and google play. This traffic comes up when doing router level DNS & traffic monitoring.

this has also been observed on an AOSP device that does not have Gapps installed.

They aren't. You are noticing videos that have a similarity to things you have talked about recently. It's the same phenomenon that occurs when you learn a new word, then all the sudden it starts popping up everywhere.

The new word thing always amazes me.. you swear you never heard it before and invariably it shows up once or twice in the next few weeks at a minimum.

This is also a great talk on the magic of science and how magicians exploit flaws in our brain or sensors (e.g. the eyes) perceive and process the environment. One of his examples is that when your eyes are moving from one focus point to the next you are literally blind and don't see anything (basically to prevent motion blur) - but your brain fills in the missing info, and so you can hide sleight of hand in these moments. One of many examples: https://www.youtube.com/watch?v=EwuRSqODRdA

There are also other explanations for this advertising thing such as you thinking about it because you saw it somewhere, having actually searched or clicked on things related to it and even if you talk to someone else and THEY search about it from the same IP address it can also end up in advertising feeds. And i'm sure many more.

There’s a name for it- Frequency illusion or Baader–Meinhof effect: (https://en.m.wikipedia.org/wiki/Baader%E2%80%93Meinhof_effec...)

No. This is not the case. It's not a new word or idea, it's a topic and content blocks that appear. Including items discussed in conversation appearing as a recommended video, despite being uploaded years ago. These are ephemeral recommendations cards that dissappear if there's no engagement at the next app launch.