It doesn't have to be an apk app that causes the adds.
It will likely be an app that you downloaded just before or about the time that the adds started that is causing the problem.
Was there anything you downloaded(doesn't have to be an APK) in the past few days? Maybe go back to check your downloads folder. @Shaggyskunk1 and @Ray2 are correct, Samsung doesn't have native apps inside their UI or system. Please keep us posted!
Malwarebytes or something similar, that usually picks them up.
also there was something I had on my device before it was called
"Opt out" I think, but I forget how I got rid of it though 🤦 it has something to do with the browser 🤷
Started using it on a Galaxy A5 then wound up buying for all Android devices myself for the ad blocking & an additional security against malware