A splash screen is needed for slower devices to display (instead of a blank screen) before the app has loaded.

I've noticed some times it even says 'react app' or something similar very quickly before the app loads (android).

Use the logo inside the assets folder as the splash screen.

If you need to assign a background colour. Use #076AE0 as it matches the logo.

Check this guide for android:
https://www.simicart.com/blog/pwa-splash-screen/#:~:text=The%20case%20for%20splash%20screens%20in%20PWAs,-When%20unconfigured%2C%20users&text=This%20should%20be%20fine%20on,initial%20perception%20of%20your%20app.

and for iphone:
https://appsco.pe/developer/splash-screens