Is it legal to hold two full-time remote jobs at once? Should I disclose?

I currently have a full-time remote job based in California. I’m considering applying for a second full-time remote position. Two different fields. Is it legal in CA to work two 40-hour-a-week jobs simultaneously? Also, should I be upfront with both companies about the other role, or is it better to keep them separate? I want to make sure I’m not violating any labor laws or putting myself at risk for “time theft.” Thanks