HTTPS://Groups.io is the feed page.
She remembers your last choice and you’re redirected to there.
So after g.io, if you go to Your Groups, that’s what will open next on g.io.
If you go to Topics. The next g.io will take you to topics.
BTW, setting a Mobile icon (group Admin settings) is the icon that shows up in the group feed. (Not when you use a mobile browser.)