How to disable a multiselect dropdown in the new request page

Hi,

I'm prepopulating a multiselect dropdown in the customer portal (Knowledge) when the customer clicks “submita re quest”. I don't want to let the customer change the value but i want them to see it.

I'm using the latest version of the Copenhaghen theme. I was trying to disable it using javascript but it doesn't work. I also tried using the props:

let result = props.requestForm.ticket_fields.find(({ name }) => name === "request[custom_fields][123456]");
result.isDisabled = true;

and it doesn't work.

What is the best way to disable it if it's possible with the new theming API?

Thanks.