Can you really not imagine how a nation state could get valuable intelligence by having an intimate knowledge of how a large portion of another nation states population is thinking?

It's an election year. Intelligence can include things like your political affiliation and level of engagement, and can be (ab)used by targeting specific areas/demographics with supportive/decisive content. Think Theil's Palantir, but controlled by a foreign government.

Quite a lot! There are articles ad infinitum about how specifically tailored the TikTok algorithm is for many users.

I certainly think that knowing very specifically what a substantial portion of a county/market’s population is interested in qualifies as intelligence.

How effectively you make that information actionable is up to the creativity of your intelligence/advertising apparatus.

Name, age, location, politics, device, amount of time spent, interests, etc.

The easiest actionable thing would be propoganda of some sort, but there's a chance of a lot of smart people working on something that I can't imagine. I'm not saying this happening, but looking at Youtube and Meta, it's not hard to imagine.

Off the top of my head you could potentially find closeted homosexuals, who could be leveraged.

Edit: Not to mention location data alone is valuable. The entire intelligence community runs on information, all of it has some value.