Okay look, I've got people commenting on this post like "I neeeeeed to multitask or I will explode" and look I get it--I have ADHD too, and I get it. But also (and you're going to hate this next part): you get diminishing returns on dopamine. Like, literally this is why the human brain is predisposed to addiction, and why ADHD brains are even more predisposed to addiction. The more you douse your brain with dopamine, the more your brain builds up a tolerance to its own dopamine and it needs more and more for you to get a pleasure response leading to further (frequently unconscious, habit-based) pleasure-seeking behavior. What fires together wires together, and habits stack. When was the last time you watched TV without scrolling through your phone at the same time? TV is already a dopamine-inducing medium, but it's no longer stimulating enough so you need to have Other Smaller Screen close by if your dopamine levels threaten to dip. Like, have you ever wondered why you're still seeking stimuli even though you're probably already over-stimulated right now? That's the diminishing dopamine returns!!
But hope is not lost!! It takes time and effort and a lot of patience with yourself, but you can gradually train yourself out of "Rat pushing button" mode. Like, okay I got sick of how I was hopelessly checking social media on my phone all the time at work, so I started setting timers where I wouldn't check my phone. 15 minutes--check phone, "Huh okay there have only been 2 blips in my activity feed. I guess I don't need to be constantly refreshing it." Then I'd move up to 30 minutes, then 45 minutes, and so on. You start with little habits, little practices. You start leaving your phone or other devices in another room when you watch TV. You set aside 30 minutes of your day for pleasure reading away from screens at a set time. You don't go full cold-turkey and move to a monastery, because then you're going to snap right back into your comfort zone.
Multitasking can also be a form of procrastination--we see a task as too big and intimidating and time consuming, so we frequently feel the need to break away from it to do something else to feel more efficient. However! You can also trick your brain into feeling like it's accomplishing more on one big task by breaking it up into little tasks. So for example:
Big task: Read this Big Fucking Chapter for my class
Set up study space (book, notepad, big glass of ice water, tea, timer app on phone, maybe a scented candle?)
Set timer for 15 minutes and put phone into airplane mode.
Pre-read: scan the chapter just reading the first and last sentence of each paragraph to get a rough overview
Start actually reading the chapter, take notes as needed.
Has the timer gone off? Take a lap. Literally get up and walk around. Go to the bathroom if you need to. You are descended from Cavemen who got all of their info input from their environment which meant lots and lots and lots of walking. Walking increases bloodflow to the brain, and the space away from the desk allows you to actually process what you just read.
Return. Set the timer again. Repeat steps 4-5.
And like, again, if your brain starts clawing at its enclosure at the 30-45 minute mark. Then you can switch tasks: work on another assignment, do the dishes, do a load of laundry, but the important thing is you're breaking the task down into manageable steps and in the process letting your brain taper down to a more reasonable dopamine baseline.