After commit CaffeineMC/sodium@19ee2f0, the transparent loading screen mixin can't be applied.

As a workaround, you can add a custom property in your fabric.mod.json as shown here: https://github.com/CaffeineMC/sodium-fabric/blob/9915466a81e9d5e32f03fe16b1902c1e4880d824/src/main/java/me/jellysquid/mods/sodium/common/config/SodiumConfig.java#L97-L114

The property would look like this:

"custom": {
    "sodium:options": {
        "mixin.features.gui.fast_loading_screen": false
    }
}

Thank you for the workaround!

Thanks for the report and a fix! I'll push an update tonight with it

Fixed in v1.3.2