How long will the disabledness last?

It's to help streamline moderation. Since there are probably enforcement team members that can't work right now they've disabled a few smaller things so they can focus on other forms of enforcement with who they do have.

why would whats happening in the real world, affect the ability to change your pfp on xbox?

I'd have to imagine a few months at the very least as I assume it'll be slow for everything to get back to normal.

Thanks for letting me know

There's been no word on that yet. Most likely it won't be re-enabled until things start to return back to normal.