For those having connection issues with Steam (9/10 people), you can follow this Twitter page or visit https://steamstat.us/ for updates.
Wonder if this has anything to do with the Destiny 2 launch on Steam with the release of the DLC today
Probably, there was likely higher server loads due to the migration. Still seems like they are having issues even throughout today from what I saw. It should clear up by the end of the week I would hope, but you never know these days with major corporations.
Most recent update from 6 hours ago:
Still no official explanation of the outages, but I will keep an eye out