ADHD involves differences in the brain systems that regulate attention, motivation and impulse control. In practice that often means attention is driven strongly by interest and novelty rather than by importance, so boring-but-important tasks are genuinely harder to start and sustain, while an interesting task can pull you into intense hyperfocus.
It is not laziness or a lack of effort. Because internal regulation is harder, external supports do a lot of the heavy lifting: visible timers, one task at a time, immediate rewards, accountability and removing distractions before you start. Structuring your environment is often more effective than trying harder.
This is general information, not medical advice. A qualified professional can help if you think you may have ADHD.