Checking and unchecking all items at once can be useful (for example, when you want to resolve the issue while the block issue transition feature is enabled.
To check/uncheck all items in a checklist:
Click on the … menu for the checklist.
Select Toggle all items.
All items will be marked as complete (including cases where some of the items were already marked as complete).
If all items are already complete, clicking Toggle all items will change all items in the list to incomplete.