Reverting to "Xbox Live Gold" after "Game Pass Ultimate" is cancelled or expires?

Ultimate Game Pass can't be converted back to Live Gold and if you cancel Ultimate Game Pass you will lose the Live Gold, so it is best to turn off recurring billing and wait for the Game Pass subscription to expire then get Gold after that.

You would be best placed to create your own thread.

If you are referring to losing Xbox Live Gold because you cancelled Game Pass Ultimate, there is nothing that can be done. It clearly states that Xbox Live Gold will be converted to Game Pass Ultimate days and can not be reverted and that canceling Game
Pass Ultimate will cancel out the converted Xbox Live Gold. https://support.xbox.com/en-US/billing/xbox-subscriptions/xbox-game-pass-ultimate-faq

You can cancel your Game Pass Ultimate membership at any time, and you will
continue to have access to your Ultimate benefits until your prepaid time ends, at which point you will not be charged again.

Note The upgrade of any prepaid time to Xbox Game Pass Ultimate cannot be reverted back to Xbox Live Gold or Xbox Game Pass, and you cannot receive a refund for Xbox Live Gold or Xbox Game
Pass. You can, however, rejoin Xbox Live Gold or Xbox Game Pass when your Xbox Game Pass Ultimate subscription ends

It states that once your Xbox Live subscription has been converted to Game Pass Ultimate days, you can not revert the Xbox Live back and that by cancelling you will lose your Live Gold. You can not get a refund and nobody in the forums can do such.

This is taken from the FAQ's about Game Pass Ultimate

How do I manage or cancel the Xbox Game Pass Ultimate plan?

You can cancel Game Pass Ultimate membership at any time: Sign in at
account.microsoft.com/services. Under Xbox Game Pass Ultimate, select
Payment & Billing, then Cancel. You’ll have an option to end your subscription on its expiration date. Depending on your subscription’s status, you may also have an option to end it immediately with a refund of the price you paid for
Ultimate only. Please note, the upgrade of any prepaid time cannot be reverted to Xbox Live Gold or other Xbox Game Pass plans and is not eligible for refund.

https://support.xbox.com/en-US/bill...ultimate-faq#506a8eac93ed49b69f17c16a5a537949

I have cancelled my Ultimate Pass and I'm happy with 12 months Xbox Live Gold membership I was able to purchase after the Ultimate Pass had expired. My original concern was whether or not I could just buy Gold or would it convert to Ultimate Pass after
previously upgrading to it, as I no longer wanted to use Ultimate Game Pass and just have Gold.

Can I revert my Xbox Game Pass Ultimate back to my Xbox Live Gold?

Do not.

what you can do is cancel your Ultimate subscription and subscribe to Live Gold again.