It seems like any platform that features link aggregation is soon overrun by bots and self-promoters trying to drive traffic, and pages and pages of link posts versus pages and pages of people talking.
Are there any lemmy instances or other defederated networks that focus on Q&A, niche communities, and people conversing, instead?
Depends what topics you are looking for. They tend to focus on particular niches. Example: home-barista.com, for coffee nerds. I’m not a regular but have posted there a few times.