How can I hide the subtasks from the board?

Hello,

To remove this subtask from the board, open this task > Open command dialog > Use the "remove Board board_name" command (please refer to this documentation section for a detailed description of boards-related commands). After that, the separate card for this subtask will be removed from the board, but the subtask itself still be visible under its parent task.

If the board adds issues automatically, you may enable the Ignore subtasks of existing cards option. If this option is enabled, then subtasks are not added to the board and are shown only under the parent task card.

I hope this information was helpful. Feel free to ask any additional questions.