I know already how to create a loading bar when I load another scene, but how to I make a loading bar for when I open the game on my phone or computer? Like before the unty splash screen.
I think you misunderstanding something:
The unity splash screen is the first thing to ever show up on screen.
After the unity splash, you can put a loading screen for the 1st scene of your game.
To my knowledge, you can’t show anything before the unity splash.