Individual users can activate a Dark Mode to enhance their experience. You can select one of the two available color themes directly on your profile page.
Settings of the App don't affect the appearance of Jira and its menu.
Available App color themes:
Changing the Color Theme
Click on your avatar at the top right corner:
Navigate to the 'My Profile' page:
Go to the 'Profile' tab:
Select a color theme from the drop-down and hit 'Save':