Many of the multitasking warnings actually refer to the concept of “task switching.” It refers to switching your attention from one thing to another.
Frequently flipping back and forth between different to-dos, is bad. It depletes your mental resources, wastes time, and will leave you feeling spread too thin.
While you’ve likely heard that it’s physically impossible to do two things at once, that rule really only applies to tasks that require the same cognitive resources. If you can find ways to combine two tasks that are different enough - like listening to an educational podcast while making your commute, practicing for a presentation while getting your miles in on the treadmill, or brainstorming article ideas while doing the dishes - multitasking can actually serve to your benefit.