Were you using the app from ZXing team
https://play.google.com/store/apps/details?id=com.google.zxi... app? Because this app was last updated in 2018, has a generic name Barcode Scanner, & has attracted hundreds of reviews like yours saying App was updated recently, & now causes Web Ads.
For a counter point, I am also using this app since 2016, & have all apps on auto update, & have never received any web add popup or notification because of this or any app.
The ZXing app is in fact the one I've had since "the dawn of android". But when I switched phones a couple years ago, I had apparently installed the one by the Space Team[1].
It took me a bit of digging to make the distinction. I have both of them listed in my App Library, and both with the same name. At some point, I believe I went to install ZXing on a new phone and Android warned me that the app may be incompatible, so I went to the space team one. It makes sense that if people aren't looking directly in their app library that they can get these mixed up and leave the bad reviews.
However, since the space team version got infected, I did try the ZXing app - no pop-ups, and it works just fine (despite the age warning).
For a counter point, I am also using this app since 2016, & have all apps on auto update, & have never received any web add popup or notification because of this or any app.