Hi it can be an app that you installed that is causing the adds. Un install any app you installed before the adds started and the go from there. If that doesn't work you will have to factory reset the phone.

Some modules you have to download from apk mirror and sideload it but everything work fine this far

I downloaded good lock fron apkmirror and it works on my s21

You can download one hander operation from galaxy store and use that to get a lot of swipe gestures on your phone use this link.https://apps.samsung.com/appquery/appDetail.as?appId=com.samsung.android.sidegesturepad