FileUpload in process, how to disable button outside panel?

I have an v2 form outside the panel with an FileUpload. How to disable a submit button, while FileUpload is ongoing?

wire:loading.attr="disabled"

wire:loading.attr="disabled"

is only working for the save process itself, but not for the uploading in background.

This is what I have tried atm:

<button wire:click='submit' wire:loading.attr="disabled">
    Save
</button>

<button wire:click='submit' wire:loading.attr="disabled">
    Save
</button>