One of the reason there is level.fyi.
Certifications help up to a certain point.
Word of mouth is still a thing for us. Linkedin recommendation, even though it's forgable?
Also, being in a company with a high engineering and culture expectation, I noticed that some people are naturally good for the business, ranging from old experienced people to non arrogant gifted entry level engineer. The more they are open-minded the faster they learn about any thing.