Unreal Engine and ASTC
Unreal Engine supports ASTC for mobile devices and other formats. To see which formats your device supports, tap with four fingers when running the game. The Console Window appears, showing the available texture formats as shown in the following image:
Open the Launch context menu to see the available options for texture compression:
The Multi option compresses textures with all available formats. This option increases package size and build time but guarantees that the best available format is chosen at runtime. ASTC can be unsupported on some devices, but ETC1 support is guaranteed.
In Project Settings, you can choose which formats are included in the Multi build variant and set their relative priorities, as shown in the following image:
For normal maps, masks, and GUI elements, ensure that you specify the appropriate compression settings in the Texture Editor, as you can see here: