In order to switch between Dark Mode and Light Mode on your Android device, follow the steps given below:
1. Open Canary Mail on your Android device.
2. After setting up an account, you’ll be able to see the below screen.
3. In the upper-left corner of your screen, tap the Hamburger icon.
4. Tap the Settings icon.
5. Now go to Reading > Appearance.
6. Click Theme > Select Dark/Light.
7. You can toggle between the two themes and keep the one that you like.
For further information:
Dark and Light Mode in Canary Mail