That is almost always incorrect. We can swap between tasks (like a computer) but we only do one task at a time.

Exceptions are things like mowing the lawn while waiting for a cake to bake or doing the laundry while waiting for glue to harden. One could argue those are still distinct tasks done separately. Super simple mechanical tasks like emptying the dishwasher while listening to an audio book also work, but even there you'll miss some details if the book has any complexity.