Having 2 jobs isn't inherently illegal. But pretty much every single full-time employment contract for an SWE that I've seen, stipulated that I am not allowed to have any other full-time job for the period of my employment.
It is purely on the employer's end, and I cannot find a legal restriction against it in any state. So it would only vary by employer.
Also doesn't the contract has something about the number of hours? It may not be enforceable, but it's on paper.
It's totally cool that we as professionals discuss our commitment and get a flexible working arrangement. It's not cool to say you will be available to respond to incidents and what not and then not do that.
It is not their concern what I do on social media. It is unfortunate that there is so much power imbalance that most employees are afraid to criticize their employers in public.
You split that 8 hours between 2 companies and unless you are significantly under-employed at both jobs (2X in both locations or more) you're not going to be able to give your all.
Why would you want to? You’re only working for money.