Typing fast matters
As much as being a software engineer is not a competition on who can type faster, I think being comfortable typing fast is a significant edge..
While you can churn out code faster if you can quickly type, the most important part is that you can rely on muscle memory to type. You can focus purely on the content of your document/business logic of your code without having to spend an ounce of effort on how to get the characters out.
The truth is that you can multi-task, but you cannot focus on two things at once. If you want to be able to write code while explaining it live (e.g. during an interview), you must be able to type without having to think about it.
This advice goes beyond just typing, you should try to reduce the cognitive overhead from any mundane tasks – get efficient and comfortable with your common/repetitive workflows. This goes from being able to swap virtual desktops, jump to an app, move windows around etc. Typically using a tiling window manager is a significant productivity boost if you have to often multi-task.
Your brain power is limited, so spend it on what matters the most.