How do you build a credible portfolio when cold outreach isn’t working?

I've worked in SEO for more than years for an agency and I'm currently between full-time roles. I want to use this time to strengthen my portfolio, but I'm running into a wall.

I tried cold outreach, sending business owners free audits and offering volunteer work and basically nobody responded.

Looking back, I get why: a stranger offering free work isn't that different from spam, no matter how good the audit actually is. Trust doesn't really transfer that way.

So I'm trying to figure out a better approach. For people who've built a freelance/consulting portfolio from scratch, or anyone in the digital marketing space:

• How did you get your first few credible projects when you didn't have testimonials yet?
• Did warm intros matter more than cold outreach for you?
• If you've done unsolicited free work before, did it ever actually convert into paid work or a relationship and if so, what made it different from "trust me bro"?
• Is it better to lean on personal/side projects with real documented results instead of working on strangers' sites?

Not looking for a magic shortcut, just want to hear what's actually worked for people instead of guessing.