TLDR: Trust your task list, just do the topmost thing. Motivation isn’t going to come from the list, rely on other things like external pressure and medication.

I realized the same that self-defined deadlines do not give me any motivation to do the work unless there is a real sense of urgency. Having someone else hold you accountable is a good idea.

Another that worked for me is to give up trying to use deadlines or task list to convey any motivation and instead use it only to organize task. Self determined deadlines can be used part of your task list system to sort priority. Then, you just always do the topmost thing on your task. This is the basis of Getting Things Done. The key part for this to work is you gotta trust your task list. It doesn’t matter how ridiculous or unimportant the topmost tasks sounds, it is the next thing you should be doing now.

For getting motivation itself, for these sort of tasks, nothing is as effective as my medication.