Since the version 0.17.0, Mixin Messenger Android adapted Night Mode. It's more comfortable when you using Mixin Messenger at night.
If your device is Android 10+, you could turn on the Night Mode on the system settings, as different brands have their own settings title, for example, Night mode switch probably under the Display and Brightness section, or it might be named as Dark Mode depends on the devices. You could search the keyword "mode" to localize the settings.
The device system is under Android 10, you could turn on the Night Mode on the Mixin Messenger settings page.
If your device is Android 10+, you can not find Night Mode on the Mixin Messenger settings page, please find it on the device system settings.