>>510824711It's actually not an advanced infrastructure at all.
The neural net that listens for audio to detect the keyword "ok google" already uses all the computing power necessary to detect and classify common words.
So it stuffs words that it recognizes into a daily log file, and it gets uploaded to servers every night or on occasion when a device is synced. Everything so far requires no detectable power usage and 1992 levels of disk space.
Google have an algorithm that matches advertisements to email addresses or profile identifiers they believe are interested in such products, and they use the keyword file as indication of interest. It gets mixed with other signals as well, it's a ratio and statistics game after all.
The only remaining part of this "conspiracy" is that they've glassed the search results on google. And if you search "is my phone listening to me to serve ads", you get ridiculously curated answers designed to gaslight you, like yours.
It's not technically difficult, it's completely possible and doable, and it would be idiotic if they weren't doing it, considering how useful it can be to advertise a product to someone based on their expressed interests.