Same!! I cannot do things like “while x is boiling, chop the vegetables.” I have to get everything prepped before I cook because I’m not skilled enough yet to be able to multitask.
Context switching makes sense when the cost of the switch is less than the time saved by doing the switch. For a beginner cook or someone whose knife skills aren't that great, maybe the cost of the switch is very high or the benefit is relatively low. Or maybe the window of idle time is not sufficient to accomplish the critical work. In this case, you just have to move the critical work earlier into the process and accept some down time.
That being said, one thing I have found is that if I'm really FOCUSING on cooking, sometimes the idle moments are larger and the context switching costs are less than I had though, and maybe I can mix some prep in with cooking. The problem comes in when you're constantly checking your phone or chatting or whatever in between the cooking steps. That can really slow you down.