You can use this tool to create a custom loading screen: https://non0reo.github.io/ImgToShader/
{% hint style="warning" %} For now it doesn't allow inserting custom logo but only changing colors and hiding the Mojang logo. {% endhint %}
If you want you can use Optifine and customize the screen with custom images.
{% content-ref url="adding-content/optifine-only-features/loading-screen.md" %} loading-screen.md {% endcontent-ref %}