Technical SEO is the half nobody checks
Before keywords, before content, before anything worth writing: can a crawler reach the page, is it allowed to, does it get the same page a visitor gets, and does the markup say what the page means. Most sites that are invisible are invisible for one or two structural reasons of exactly that kind, not for a hundred small ones.
A technical SEO audit here is five days of reading your site the way a crawler reads it: an actual crawl, index coverage compared against what exists, Core Web Vitals measured on real page loads, structured data validated rather than glanced at. The output is a list ranked by impact and written so your own developer can work through it.