I’ve heard many stories similar to that. There was even rumored for a while that advertisers where using frequencies that were out of the range of human hearing that would commutate with other nearby devices for advertisement influencing purposes.
The way advertisement works these days has to be borderline brainwashing these days. I know some people who are so easily influenced by them they seem to have an addiction like symptoms to spending and buying not so needed things when they already are struggling.
I always find it interesting how fast me searching for something on newegg or amazon and that exact item now follows you around for quite a while in advertisements. Even more interesting was when I bought something and the ads for it followed me around till it was shipped a few days later. Then suddenly they stop showing up. As if they wanted to prevent another similar product from showing up and convincing me to cancel my order and buy that product instead.
I have also noticed as you have how tailored search results become depending what you are logged into.
So yes. They are knowing more about us than we know even of ourselves and yes, all that you mentioned is just it. Just it!
Some say they use to influence even election decision-making. With that much information about us, on a general level, they can influence anything. That high frequency thing you mentioned is very possible really. With google especially, they have that much power, looks like they rule the internet. I still use their browser alot though and ofcourse gmail, youtube etc, so how won't they know so much