Should I try to complete the boring thing that used to be interesting, or should I start creating the new interesting thing that I probably won't finish?
put them both in a list. then go on a short walk to figure out which one you should work on. if/when you work on the boring thing, the first thing you need to do is figure out if you can make it good in any way, and if you can't then you must cancel it. when/if you work on the other thing, just figure out what it needs next. save your progress and if you are feeling restless you can generate ideas for other new things also, and put them in the list