By default, the Unscheduled Drafts sidebar is closed when you view the calendar and can be toggled with the button.
If you’d like to keep the sidebar open by default, start by visiting the Settings menu. Then, locate the option Keep the Unsched Drafts sidebar open by default, and click the toggle button.
Then click the Save Settings button to finish enabling this setting.
When you return to the calendar, you’ll see that the sidebar is already open.
If you’d like to close it, you still have the option to click the Hide Unscheduled Drafts button, but the sidebar will always be open by default now.