Ok guys, I have a technique for connecting to Google!
1. Install the modified app, and go to the login screen that displays your Google accounts. Don't click on anything.
2. Then go to Google Chrome, then to the official webstore of dokkan (bandainamcoentwebstore.com/dbz-dokkan-ww/fr)
3. Log in to your official Dokkan account with your Google account.
4. Once logged in to the webstore, go back to Dokkan and click on your Google account linked to dokkan
5. It worked for me!

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If this doesn't work for you, I'm sorry. I'm on Samsung S25 Ultra with One UI 8.5, with up-to-date Google Play services.