only get bored with the project after the hard part is done

Ah yes, the ADHD prioritization list…

1. Interest
2. Novelty
3. Challenge
4. Urgency

It’s because ADHD people don’t get any “ah, it feels good to complete this thing” dopamine for mundane tasks, and only get it for doing big tasks.

If they’re interested in the thing, then they don’t care about the dopamine reward; The task itself is the reward. Lots of ADHD people will have their comfort games or shows that they can focus on for hours at a time.
If it’s not interesting, it needs to be novel. Learning something new rewards that dopamine in a way that simply doing the task does not. And being challenged in new ways means you get dopamine rewards even for otherwise small tasks.
If it’s not interesting or novel, it needs to be challenging enough for your brain to consider it a large task worth rewarding.
And finally, if it’s not interesting, novel, or challenging, your brain can substitute adrenaline and cortisol in place of dopamine. So the task needs to be urgent enough to trigger those stress hormones. Every person with ADHD has stories of doing a week long project in three hours, because they put it off until it was so stressful that the stress was its own motivator.

If the task doesn’t hit one of those four basic points, it simply won’t be prioritized.