I once worked with a mathematician in a research group who said, "Multitasking destroys me". I did not know what he meant at the time, but I do now.
If your job is to be "on the bottom of things" doing careful calculations and designs, you should not multitask. But if your job is to be "on top of things", then you will have to.
Can't mix the two safely.
You do not want the engineer/architect calculating the load on a beam to be checking email, on slack, answering the phone and other "on top of things" tasks.
But some managers think you are a slacker if you are not running around with your hair on fire at all times. They don't understand the difference.