Switching tasks means stopping one thing and starting another. Stopping is hard when you are absorbed, which many people with ADHD describe as hyperfocus. Starting is hard because of task initiation — the gap between knowing what to do and beginning it. A transition stacks both, on top of time blindness that makes the upcoming switch feel abstract until it is suddenly urgent.
What tends to help is making transitions predictable: warnings before a block ends, a short ritual between tasks, a note about the next step before you stop, and fewer switches overall by batching similar work.