Hi, updating.
You can add splashscreen with Unreal Plugin Language | Unreal Engine 4.27 Documentation.
This extension enables us to customize the AndroidManifest.xml. Go check the link.
Also, I found the so useful plugin Sovahero/PluginMobileNativeCode (github.com) that you can display splash screen and even execute Java code with it. I strongly recommend you use it🤞.