Single-page apps (SPAs) using client-side rendering (CSR) like React do get indexed by Google, it's just not instant. Depending on how long it takes for the content to load, the Googlebot might not be able to figure out the correct on-page SEO.
If SEO is a critical requirement, I'd recommend either server-side rendering (SSR) through a framework like Next.js or completely static sites through whatever framework you prefer (Next.js, Gatsby, 11ty, Hugo, Jekyll, etc, etc).
If SEO is a critical requirement, I'd recommend either server-side rendering (SSR) through a framework like Next.js or completely static sites through whatever framework you prefer (Next.js, Gatsby, 11ty, Hugo, Jekyll, etc, etc).