Lol okay, this isn't easy to do because the tab underneath moves out of the way like 90% of the time. I cannot figure out why it doesn't sometimes. I also just now somehow managed to create a tab group with just one tab. The tab group dialog popped up when I just released the tab without any other tab underneath. Also the opposite: I dragged the tab onto another tab, there was a blue highlight indicator and everything, I let go, but it just moved the tab anyway without grouping it. That's some serious jank.