Are there any communities for solution architects?

If you mean solution architect in the sense of sales engineer or technical pre-sales, it could be worth checking out the PreSales Collective [0]. I'm a solutions engineer myself, they are on my radar to look into, but I haven't done it yet. They were recommended to my by a colleague.

[0] https://www.presalescollective.com/

I'm pretty sure I do a lot of "solution architect" work, but I still don't self-identify as one and have very little idea what it means. I think it's one of those titles that big tech companies (and consultants) use, but are kind of lingo-y and not really tied to reality.

For specific questions, I've seen some great questions and answers on Stack Overflow.

Affordance aims to provide an expert community for helping with startups. We are very early and thus do not have architects yet, but looking to add this domain.

https://affordance.app https://twitter.com/affordancehq