you know that zero texting apps nowadays use native input anyway right? even native apps will implement their own input and it's always awful, but the pm needs those style previews... (you're still right thought)
Too lazy to check on android rn, but I recently worked with the apps/chats on it and entered text, it didn’t feel different.
whatsapp is the poster child of this technique btw.
So yes, compared to HTMLInputElement these are absolutely custom. But for a platform, absolutely native.