Definitely disagree. I used to feel terrible about not being able to multitask. Then I found out no one can truly multi-task! Generally, saying you can is more of a measure of confidence (earned or otherwise)
Slightly agree. I also have ADHD. Sometimes I need to be multitasking for things to get done, e.g. exercise, cleaning, showering are basically impossible if I'm not streaming something or at least listening to music.
If I'm studying, I need zero distractions, and that includes music, even if it doesn't have lyrics. I also tend to hyper focus on games, so holding conversations while playing is very difficult. If I'm staring at my phone, I'm probably too focused to even notice someone come in and start talking.
If the meal needs me to attend to more than 1 kitchen utensil, something is getting burned. If you want to talk to me when I'm doing something, the something isn't getting done. I had a job where they wanted me to talk on the phone and type a description of the call at the same time, and, no way José, not if it's important that either include coherent sentences.