> For example my employer doesn’t provide a work Github account… but while I have the option to use my personal one, I can also sign up for a separate one.
Apologizing for being the Well Actually Guy, but GitHub's terms of service include the line "One person or legal entity may maintain no more than one free Account". If your employer doesn't provide a work account for you or use Enterprise GitHub, then technically you can only have both a personal and a work account if one of them is paid. My suspicion is that GitHub doesn't go out of their way to enforce this, but it's there.
As far as Apple IDs go, there's absolutely nothing that prevents you from having multiple ones, though, no. I think I've had work Apple IDs in the past. You can also have separate Apple Store accounts and Apple ID accounts (which I do, although that's something of an accident of history in my case). While I've logged into my Apple Store account on a company-owned device so I could use some of my personal applications (ones that would be appropriate for work, for the record), I would absolutely not want to log into my personal Apple ID -- the one that accesses my personal mail, calendar, iCloud Drive, etc. -- on a company-owned device.