Brainstorming is mostly seen as a group activity. Doing it alone is also very productive, often times more so. This will enable the best of both.
An app that everyone in the group uses. Each member has a given amount of time as decided in advance to brainstorm alone, writing and sketching his ideas in the app, each one as a separate “card”. When the time is up, all the members see all the cards. They go through them, and either vote on wich ones they like (probably on the last round), or just get new ideas from them. Then another round of private brainstorming follows. Do it until you all decide it’s enough.
From time to time, you’ll feel lonely. You’ll feel you’re all alone and you have no one or no one understands you.
Have a place where people can volunteer to “be on call”. When someone reaches out because they’re lonely, they’ll write a little about themselves, and those who volunteered and are available (you can “check in” that you’re available) get an alert and can see if they want to help, and make contact if they do. All done anonymously.