I missed posting notes when this went out, so here's a quick catch-up. These changes are already live.
You can switch between Global and Friends leaderboards from the home menu. That choice carries across the daily challenge and ranked modes, and Slurdle remembers it for next time.
The little globe / friends button opens the picker. There's also a short explanation in there if you're wondering which scores you're looking at.
This was part of the October 25 update. Sorry for the late notes!