You probably discussed it because you were aware and interested in it, and your awareness and interest showed through in your other trackable habits outside of your chatroom. You only notice when they guess your interests correctly.

whatsapp is owned by Meta. I did a quick DDG search to see if I was correct and got this:

"Meta owns several companies, including Facebook, Instagram, WhatsApp, Messenger, Threads, Meta Quest, Horizon Worlds, Ray-Ban Stories, Mapillary, Workplace, and Portal (discontinued)."

I've been working to get the people I communicate with on Signal.app, instead. Other more informed individuals may be able to make additional suggestions.

The reality is actually far scarier...

Meta manipulated you to have those conversations.

Keep nefarious apps in your work profile and don't store any files in your work profile. Turn on the work profile only when you use the app, then freeze it again as soon as you're done. Regularly clear the apps' caches. This will limit what the spyware can spy on and how long they can spy on you.

It happens to me as well, in my instances it's most likely the social network they tied me to. Some friends of mine are heavy Instagram users and whenever I hang out with them I get almost real time relevant ads on my isolated Instagram.

Just read most of the comments here and I feel nauseous about this.

My job encourages instagram use.

I think the only way around having our devices spy on our spoken face to face conversations is to have a mobile device with a removable battery. Who remembers the HTC EVO and all the phones like those? Anyone know of a good phone that offers the removable battery?

Use it only through your web browser or bite the bullet and don't use it at all despite those people that are currently on it. Maybe explain in a meme why you are leaving and where you can be found.

Use the user profiles feature of grapheneos to make a "social" profile and only use that to access Instagram / facebook.

Meta sells your convo data on WhatsApp for ads, if you use it you will get targeted ads regardless.

Other options are signal (Molly on fdroid), simplex, etc.

Probably because your friends search about it when they are not having things separated and based on the social graph that IG thinks you're interested in it too?

I don't think Instagram can read your Matrix conversations, but may be able to predict your interests with fancy algorithms or buying information from data brokers, even if it's related to things you did on another device.

If you want to be more sure it's not spying on your phone, uninstall the app and use it through your web browser.

Its really hard to tell from a technical perspective, especially without having closely monitored all of your digital activity (and those that you have been in close contact with) in the days/weeks leading up receiving the ads. Some things that Meta could have done (in varying degrees of realism) include:

• read anything you downloaded from your Matrix client, like file attachments
• read your notifications if they contain any contents of the conversation
• read your clipboard if you copy/pasted anything into/out of a Matrix client
• actively participating in the room and associated your Matrix ID to your Meta account(s)
• scraped the contents of the room if it is public and unencrypted
• others in the Matrix room saved your Matrix ID in your contact information within their contacts
• Meta is recording your screen outside of Meta's apps
• a Meta library is used in another app/service on your device that is sharing information back to Meta
• read an attachment that you downloaded elsewhere then shared on Matrix
• Meta read screenshots you or others took of the conversation
• Meta has a back door in the Matrix server or client software used
• the administrators of your Matrix home server (or the administrors of any other home server in the room) are sharing non-encrypted information to Meta to offset hosting costs
• Meta is running a home server of a user in the room
• you or someone you are associated with clicked on a link shared in the Matrix room that contained a tracker or led to a site that contained a tracker

Its really hard to comprehensively and conclusively avoid all "spying" that Meta/Instagram could do to you. The best thing that you could do is something that many people aren't capable or willing to do - not install any Meta software, don't use any Meta services, block any Meta IP addresses and/or domain names, and advocate that those around you do the same.

Realistically, the best advice that youre going to get has already been said. Use the web browser instead of the app as much as possible, ideally in a different browser and/or user profile. If you must have the app installed, keep it in a separate profile and kill the app and/or profile whenever it is not in use. Review all of your security and privacy settings in all Meta apps. Review any apps/services you allowed Meta to connect to/from (and the security/privacy settings of those apps). Reduce the amount of information that you enter/share on Meta platforms. Review the other users that you are connected with on Meta's platforms.

Use a modified app of Instagram.

Is IG on a completely different profile in GrapheneOS, or is the app installed on the primary profile where you use your other apps? GrapheneOS's profiles completely isolate from one another.

If you want to be extra safe I guess the best way would be to use the web version of Instagram with ublock origin installed. If you can find a way to use Firefox containers on Android as well it could really restrict what they can access.

Use Instander.

Maybe Instagram has access to your keyboard so it can monitor what you're typing in other apps.

Could this be related to Off-Facebook Activity?

If the only thing you use it for is chat, I think you can chat with instagram users on FB messenger instead, which you can then heavily restrict in terms of the OS permissions you give to it.