Also a lack of LinkedIn account makes you more suspicious and less likely to get hired. So this is additional value in having an account. For appearances.
Yeah I recently heard about people working multiple jobs at once - I wasn't surprised - with work from home being a thing and many jobs at big companies being not overly strenuous, you can get away with it.
A previous coworker had been not especially good at his job and left after two months, and a little later I went looking for his LinkedIn to see where he'd ended up. Couldn't find him but didn't give it much thought. A friend told me that he was working at a company up the street but was also working another job at the same time, and the penny dropped - you can't have LinkedIn and be working two jobs at once and reasonably expect to get away with it or get hired again.