Your WordPress site can be slow before PHP runs. That is the part many builders miss. Before WordPress wakes up, the browser may already be dealing with:

- DNS lookup.
- TLS negotiation.
- HTTP version.
- Connection setup.
- CDN routing.
- Cache rules.

Performance is not just a WordPress problem, it is a stack problem. It's one of the core tenants of my Make WordPress Fast course. Learn the whole system:
https://withinwp.com/courses/make-wordpress-fast/