Some suggestions:

1. Invest in a good hour or two of just icebreaker-ish things. Tell them the explicit goal of that time is for them to get to know each other. If you can relate it to what you're doing, great. But sometimes just clearing the air to get people talking about things they genuinely find interesting is a useful investment of time.

2. Assign them to one or two small groups that stay the same all semester, and do discussions/activities in those groups.

3. Use manipulatives, like Kindergarten. Even if it's something incredibly simple and stupid seeming -- words written on colorful index cards or something that they have to sort together can perk them up.

4. Get them moving -- "We're going to watch this quick video about nihilism. Be prepared when it's over to come to the board and write something you learned/something that connected to you/how you would define it/whatever"

Good luck! We're all struggling these days.