Ordinarily, I recommend doing a difficult task first when you are still fresh. But on a day when you simply cannot bring yourself to do anything at all, I recommend going in the opposite direction. List everything you need to do and pick the easiest thing. Get that one thing done. Then reward yourself in a small way, but not a way that will lead to further distractions. Do not reward yourself by watching TikTok - that path will suck you in and lead you nowhere (at least in terms of your to-do list). Reward yourself with a handful of m&ms or something.
Once you've done one thing, it might get easier to start on that to-do list. Research shows that setting small goals and accomplishing them releases a dopamine boost to your brain. If you're still struggling to get into a deep flow of work, pick another small goal and do that one next, then give yourself another small reward.
If checking off two small goals still doesn't get you in the flow, it may be time to accept the reality that today might not be your best day. If this is looking like the case, then it's time to prioritize the things that absolutely MUST get done. If you're only going to accomplish a few things in your day, then make it the stuff that is absolutely necessary and for which there could be large consequences if you fail. Not every day is going to be your best, most productive day. You are not a robot. Some days are going to be days when your brain and body need rest. If today is one of those days, then it's time to do the bare minimum. That means, do anything that is absolutely REQUIRED and cannot be postponed - the assignment that is due tonight, perhaps. Then just call it a day. Some days you're going to knock it out of the park and accomplish everything like a freaking rockstar, some days you're going to do the bare minimum. If today is a bare minimum day, then do not sit at your desk, staring at your computer and feeling bad about yourself. Do the minimum to get by, then give yourself a break. When you sit at your desk and do nothing but feel guilty, you waste your day entirely because you neither accomplish anything nor do you get the rest and respite that you so obviously need. If today is not your work day, then go out and find some joy, some rest, and some peace.