For small SEO agencies, freelancers that don't put a ton of energy into their own SEO (whether it's too competitive or you rely on word-of-mouth), I highly recommend LinkedIn for lead gen.
After optimizing my profile, I have been generating 3-5 leads from LinkedIn per week WITHOUT posting, and at a higher close rate than any other traffic source.
I think this is an awesome platform because the organic reach seems to be better than on Facebook and it doesn't require constant posting like on Instagram (though I highly recommend staying active for better results).
There are also some pretty big players on the platform - I have landed some $10k+ SEO outreach gigs at major companies that you never see hanging out at Facebook or Instagram.
Have you seen solid results from LinkedIn lead gen?