This task has no pieces yet.
A task is finished when every piece beneath it is signed off, so it needs at least one. Anyone can break it down — you do not have to be the maintainer.
Break this into pieces first — a task with nothing beneath it cannot complete.
There is no button here to mark this done. A task completes when the work beneath it is signed off, so the state always reflects what has actually happened rather than what someone declared.
At most 4 people hold pieces of one task. Small groups finish things; large ones negotiate. The maintainer is not one of those places — they set the task up and sign off.