Getting your first ten clients without a portfolio
You cannot get clients without results and you cannot get results without clients. The way out is to generate results that do not require a client, and to sell to people who are not comparing you against an agency.
Rank something of your own first
Build a small site in a niche you find interesting and rank it. This takes a few months and produces the one thing you cannot fake: a Search Console screenshot with your name on it.
It also teaches you what the work feels like when nobody is paying you to guess, which is a better education than any amount of watching.
Sell to businesses you already have access to
Your family's business, a relative's clinic, a friend's shop. These are not embarrassing starting points, they are the standard starting point. The access problem is solved and the trust problem is solved, which leaves only the work.
Charge them something, even if it is small. Free work is treated as free work by both sides.
Lead with an audit, not an introduction
Cold outreach that introduces you gets ignored. Cold outreach that opens with a specific, observable problem on their site gets replies, because it demonstrates that you looked.
The audit is doing the sales work. Do it well, present three findings rather than thirty, and connect each to a business consequence rather than a technical one.
Subcontract before you sell
Agencies routinely have more delivery work than capacity. Subcontracting pays less per hour than direct clients but the sales cost is zero and the work is real.
Two or three months of subcontract delivery gives you both income and cases you can describe, subject to whatever confidentiality applies.