Some checklist actions like editor or templates are not available on mobile due to limited screen size.
Jira mobile shows the checklist only if the checklist panel is displayed on the right side of the desktop browser view. Therefore, to make the checklist available in Jira mobile app to:
When the checklist is enabled for Jira mobile app, you can see it as presented on the screenshot below:
When you click the "Issue Checklist" element, it will open a new panel as presented below:
To access the edit, delete and reorder actions, please touch the checklist items anywhere within the text area/row:
If you enabled dark theme in the settings of Jira mobile app Issue Checklist will respect that setting and will also switch to the dark theme.