You have most likely downloaded a malicious app that is the source of these intrusivefull screen ads/redirects. You will need to identify the offending app and delete it.
☆ Scan your phone for malicious apps Go to Settings > Device Care > App Protection Scan Phone. This will identify any potential threats to your device.
☆ Use Samsung’s Nice Catch app If you are getting intrusive ads, pop ups, etc, Nice Catch can help identify the offending app so that you can delete it.
Turn on the various categories in Nice Catch.
When the undesirable behavior happens again, check Nice Catch to see which app triggered it.
try turning on safe mode. you can do this by swiping from the right corner and press that power button on the right. once you get there, select restart. hold restart until it says safe mode. what it does is to block any third-party apps you have installed. once you restart your phone, you will see safe mode probably on the bottom left of your screen. now you can uninstall the apps that is keep showing ads.
Do as @CEParsons recommended and use Nice Catch. Turn on the options for "detect toasts" and "detect commercials". Next time a random ad pops up, open Nice catch and see which app it came from. Once the app is identified, uninstall it. If you have a carrier device, some of them are now starting to send pop-up ads instead of just installing apps on your device, or it may have installed a game that has some malicious code in it.
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