Just update for anyone interested or encounter this problem as well.
I did a factory reset and it actually resets back to whatever backup you have. I have auto-back up so it backed up to the previous week. I lost all sms (text) messages that happened after the previous week. I also lost all pictures/gifs sent in any message dating back to the beginning. It deleted all photos/videos/documents downloaded dating back to the beginning. It deleted local storage of photos taken with the phone dating back to the beginning (the photos are saved on google though if you have them uploaded to the cloud).
When I say beginning, I mean beginning of having the phone Pixel XL.
So in conclusion, Factory reset did what I wanted, stopped the popup ads. But I lost all pics in messages but was only able to save conversations from week prior to this one. Everything else is gone. I didn't have any music so it's ok, and all the pictures/videos I took are on the cloud. So it went well.