As many others have mentioned, there is an exception in California for things done using no company time and resources, and unrelated to your work or the company's area of business or "future anticipated research". This exception required by California law is often copied verbatim into employment agreements, even if you are working outside of california. However, the last clause of this term essentially de-fangs the term entirely if you work at any medium sized company.

I have worked at two FANG companies, and in both cases I crossed off this clause from the contract and initialed the line before I signed it. I told them that I couldn't sign that line and what I did, and in both cases, they said they would "get back to me" with what legal said. In both cases it never came up again, and I started working having signed only the modified contract.

I think that's a fair comprise of who owns what, and I would suggest anyone else to do the same thing I did.