Cancel PC Game Pass - not offered refund option

You would have to cancel the Core subscription (and refund if available) and then purchase PC Game Pass.

No. It wouldn't convert like that. You'd either just have to buy PC Game Pass separately, convert to Game Pass Ultimate in order to have both, or try to cancel and refund the Core subscription and then buy PC Game Pass.

Hello Fe, this is Manuela!. I'm an Independent Advisor and community user like you, ready to assist with this.
Not a Microsoft employee.

At the moment, it is not possible to switch between PC Game Pass and Console game pass.
I can suggest you to upgrade temporarily to Game Pass Ultimate and once the subscription ends, subscribe to PC game pass.

Another option is canceling the subscription only if the system shows that you're eligible for a refund. You can try this by visiting the next link:
https://account.microsoft.com/services > manage subscription > cancel subscription

When you added the Ultimate, the PC Game Pass was cancelled and upgraded to Ultimate. So it was no longer eligible for a refund.

If you bought the standard Game Pass, then I believe you would need to cancel and refund the console one and then subscribe to the correct one. If you bought Ultimate, then it includes the PC version within it

To cancel, you need to go here:

https://account.microsoft.com/services

That should land you on the subscription page of your account. From there, you can cancel the GP and it will give you the option for a refund if that's available.

This page covers refunds:

https://support.xbox.com/en-GB/help/subscriptions-billing/buy-games-apps/refund-orders