Hey exhanek,
If you install the latest version of Wurst for any Minecraft version, including 1.20.4, then you can turn off the logo and there won't be any "outdated" messages.
If you install an an outdated version of Wurst for any Minecraft version, then you will see an "outdated" message in-game and you won't be able to hide the logo. This is intentional, because you need to update.
The download page on WurstClient.net will also warn you when you're trying to download an outdated version, with a link to the latest version that you should install instead. Here is an example:
If you install any version incorrectly, then Fabric will give you an error message. This message usually tells you in plain English what is wrong and what you need to change, but I've also written a guide explaining each of the possible error messages and what you need to do if you see them: https://www.wurstclient.net/tutorials/how-to-install/wurst-7/#launch-fabric-error
Hope this helps!