2FA code created with the same name for all users. So if you want to have more usrs in your phone app, previous is overwritten as it same. I would recommend changing
plugins/login/classes/TwoFactorAuth/TwoFactorAuth.php
line 69 from this:
$label = $username . ':' . Grav::instance()['config']->get('site.title');
to this:
$label = $username . ':' . $username . " @ " . Grav::instance()['config']->get('site.title');
this will create unique entry for each user even on the same device