Including Facebook, apparently. About 90% of Instagram ads were irrelevant to me for about two years. Then I mentioned an interest in photography in a private conversation, now 75% of ads are photography-related.
Saying "crap ad tech" is giving way, way too much credit to ad tech. I'd argue current ad tech IS crap, because the overall methodology and approach is fundamentally crap.
The problem is that the entire advertising industry is crap and has successfully contaminated and taken over the tech industry. The only way out is regulation so that 1) advertisers are liable for what they display (to discourage scam or illegal ads - and in some countries NSFW content would fall into this category as you're supposed to ask or verify the user's age) and 2) privacy regulations that make targeted advertising opt-in so that overall the cost of advertising becomes too great and starts allowing alternative monetization models (such as actually asking the user to pay for the service) to compete.
What's more likely?
1. You mentioned thousands of other things in your private conversations. They suddenly start to narrow down on one specific one. 2. You're interested in photography, and are using service made to share photos. You follow photography accounts/search on the internet for photography related content, this signal got picked up, you clicked on some ad (by mistake most likely), and signal got amplified.
1. I distinctly hadn't mentioned photography in private or public messages. Ever. Nor had I tagged any of my camera equipment in any of my posts. Hard to believe, I know, but I created and manage the account with explicit intent and action, preferring to move personal conversations off-platform.
2. I don't follow photographers, and prefer to only follow certain friends. While I don't go to that great an extent of concealing my browsing history, I also make some effort to segregate information flow. Plus, the low-hanging fruit of Firefox + DuckDuckGo + uBlock usually does a decent job of helping with that.
3. In the two years I've had an account, I hadn't seen a single photography-related ad prior to the conversation on photography. Ads typically revolved around random tech products (many of which were irrelevant) and ads for TikTok (zero interest in it).
4. There was a dramatic shift in the content of ads within 24 hours of the conversation on photography. It's conservative to estimate 75% of ads are photo-related. I have a hard time remembering any other ad (a sign of their irrelevancy, in my opinion).
5. Given the demographics of this site, I'd appreciate (for myself and others) if you'd give at least a little bit of benefit of doubt on technical comprehension.