Disclaimer: I used to work in this industry for about 4 years at various DSPs. I've worked with Grindr as a client and bought a lot of Mopub inventory and met with their employees several times.
DSPs get access to around 84 data points from the various SSPs that they work with. This ranges from information around age, sex, city geolocation and what apps are currently installed on your phone. It's scary to see just how effective these 84 data points are in predicting user's likelihood to commit certain actions.
My friends that are still in the industry are quite confident that Apple will depreciate the IDFA in the coming year to fit more with their 'privacy that's iPhone' stance. This will greatly reduce the ability for DSPs to target users and all performance marketing on iPhones will be reduced to branding ads, that have very little targeting.
As a consumer, I'm very happy with these changes and hope Google will follow suit with the GAID. If you're using an iPhone I'd recommend to switch off your IDFA in your privacy settings ("Limit Ad Tracking" toggle on). By doing this DSPs will no longer be able to target you.