As for getting fired, I've never been fired but I've also never been caught. Getting kind of good at it, doing this for the past 5+ years. I would assume the nice thing about getting fired in this situation is having multiple incomes to fall back on. I've never had trouble finding new jobs.
Maybe call it the "144 Hour Work-week"
I don't doubt that some contracts state you can't work another job, but I would consider rereading some of your contracts. Especially in work friendly states, it's hard to enforce those types of clauses and companies are really good at wording things like it's a restriction when it's really a legal suggestion.
> and they found out
How exactly would an employer easily find out? I also worked multiple jobs at FAANG level big tech, you would have to explicitly say something to get found out. In fact, the big tech jobs I've had were genuinely the most administratively bloated and least likely to find out.
Also, finding a new job has never been that difficult, especially in this market.
However, you are likely in violation of employment contract. Where I currently work, and my previous job, you could actually find a way through the official channels by just not being totally accurate about the other job(s).
If challenged it comes down to the details. Moonlighting is a perfectly normal activity for driven people (I did tech blogging for a previous employer once while employed by someone else, so I have navigated this system at one company), and by structuring your disclosures very strategically you could likely avoid any legal impacts.
All that said, working multiple jobs like that will definitely get you fired if you are found out. Even in a state with strong worker protections.
And again, all that said: Don't do this.