I have a Firefox extension for creating PWAs (Progressive Web App), and had a profile setup for Youtube. The adblocker detected popup just appeared a couple weeks ago. So i just deleted the YouTube PWA profile, recreated it, and added Ublock back. Havent seen the popup or ads since.
Download the ProtonMail apk from a trusted place such as APKMirror, and then use Revanced Manager to change the package name. Install the patched app and profit! You can do this over and over again.