How to find clients for Web Performance Optimization?

So turns out that website speed really matters, as in bounce rate for sites that load in 2 seconds on average is 9% but for sites that take 5 seconds it's 38%. There are many more facts that prove that faster sites have more conversions but I will leave that for another post.

So I am focusing my business on Web Performance Optimization and can push a Shopify store to a +90 score in PageSpeed Insights.

So I am sure my product is valuable but the question is how do I find clients?

I created a Pitch deck explaining the product to people I know and they seem to like it but most of them are DIY kind of people, not that I think they will succeed since there is a lot that goes into it.

So how do I find clients?

Should I be doing cold outreach (calls and email)?
Or focus on SEO and content creation?
Is there a better option?

Also, I am currently based in Vienna Austria (don't speak german tho) and cold outreach is not completely legal, so people have advised me to stay away from cold emailing. O and knowing my email account might get marked as spam doesn't help that either.

I know all of these a valid options but if someone has experience in these topics it would be helpful.

Any advice is really appreciated,
My site is deep-blue.io which probably needs to have a page specific to this product but since I don't think I will get any sales at the beginning through the site I haven't gotten around to it.