Lifestyle gurus these days love talking about how multi-tasking is a myth, that people can't multi-task, but instead, just switch their attention rapidly between different tasks. And therefore we should do only one thing at a time.
That is multi-tasking. At least that's how computers do multi-tasking. (ok, there are exceptions, especially as computers take advantage of multiple processors) but that is by and large how all personal computers have handled multi-tasking. (that was one of the first lessons I learned about computers back when we were first upgrading from DOS to Windows 3.0... not even 3.1).
And if that kind of multi-tasking has worked for computers, I don't see why that's an argument that humans can't do the same.