Today my friend said he wished he had this conversation with me years ago, so I’ll recount it for all the similar people who aren’t going to have it in the next several years. (I expect people to be relevantly similar if they are ADHDish and not prone to smoothly doing the stuff they set out to do.)
Often if I achieve something arduous, I award myself some kind of predetermined nice thing, such as a sundae.
When I discuss this with other people, they tend to say things like “but I can just eat a sundae anyway”, which I hear as meaning that the issue is that that they have no ability to stick to their commitments and not acquire the sundae unless it is earned. But on further discussion, what this friend meant at least was that since there isn’t any rule against eating a sundae any time he wants without doing something arduous, it isn’t a very compelling impetus to work.
While I do usually treat the reward as disallowed in the temporal vicinity of it being a prize, that isn’t the important difference here in our models.
I’m just not at all expecting a sundae to be a sufficient incentive to work hard for hours. Winning at a challenge, and at achieving my goals in particular, is compelling in itself. The prize for winning is more like a decoration accentuating, concretifying and glorifying the win, which might otherwise be an abstract and anticlimactic point.
So if you think you are the wrong kind of person to make use of concrete prizes for achievement, due to not being incredibly compelled by the kind of stuff a child with no money would work hard for, perhaps reconsider.

We have forgotten the psychic importance of rituals and symbols. Important for psychic health long term. Thanks for the reminder!
I was expecting you to give *my* response to that common objection, which is that it works as a habit-building incentive, not an "Omega offers you a choice" incentive.
Operant conditioning works at a System 1 level. I'm not rewarding myself (a rational human who can obtain ice cream whenever he wants). I'm rewarding the lizardbrain part of me that's in charge of my habits, which *doesn't* get to have ice cream whenever it wants (≈always).
And, crucially, the reasons I usually deny my lizardbrain ice cream are things like "it's not very healthy" and "I would have to go get it from the freezer" (let's not discuss which of these is more load-bearing), which are not the kinds of disincentives the lizard cares about.
(This explanation probably works better for things like "eat some candy right after / while doing an annoying work task", not "ice cream celebration of finishing a big project", which I agree is basically decorative/hedonistic. It also probably works even better with nicotine but haha no.)