After having worked at four startups, including two as CTO, I have zero remaining equity or financial upside from any of the startup equity. This is the bitter take away, your equity will most likely amount to nothing unless the company is on a clear path to IPO/ acquisition or a promise of share buy back during the time you're at the company. This is a higher bar than simple profitability.
The reason you work at a startup is because you
1. seek to start a company in the future and want to index on the mistakes of the startup you work at
2. want to grow in responsibility/ leadership because you're bored at BigTech
3. want to learn more and apply the learnings, hopefully also experiencing the exhilaration that comes from hockey stick growth
The advice to my younger self would be to ignore startup equity if you're an employee for all practical purposes. The only concrete indicator that equity signals is the trust your founders have in you.