- Ads you see where?
- Are you talking about ads provided by App Developers?
- Are you talking about ads you see on web pages?
- Do you have a Google account?
- Are you talking about Ads you see in Apple products, such as News or the App Store?
The Ad Identifier is used by apps where they could request it to monitor the ads that were previously served to you. The fact that they are now random means that those developers cannot sell your identifier to others and is for your protection. That is a good thing. You no longer have the option to change it, because it is automatically being changed without you having to do it.
For Personalized ads that Apple uses, you can review the information collected and also turn it off if you wish.
Control how Apple delivers advertising to you on iPhone - Apple Support
For more information, you can review these Support Articles and also view what information is collected by Apple:
For apps in the App Store, review the Privacy Nutrition Label seen for every app that details what data is collected. It is your choice if you want to download the app at that point. In my opinion, I would stay away from every Social Media app. Once you have an account with that developer, then they know every post you like, track everyone you follow, and everything you search for on their platform. That is the information they use to sell to advertisers and not controlled by Apple at all.