Failed to get the 'mode' property on 'Request'

I’m sorry if this is the wrong place to raise this, if it is I apologize and would love to be directed to the correct place. I’m working on a SvelteKit application being deployed to Pages, and when calling fetch I get Failed to get the 'mode' property on 'Request'. It seems Workers doesn’t provide this (and the credentials property). Is there a reason for this, and perhaps a workaround?

There is an issue about this on SvelteKit: Error when doing external fetch on Cloudflare Workers · Issue #6739 · sveltejs/kit · GitHub (note the workarounds here don’t work for Pages)

The reason is that the fetch API that workers uses doesn’t support those two properties.

I understand that, is there some way to polyfill it or something?