Used it last week.
Our airbnb for Lisbon cancelled 5days before stay.. All hotels were sold out due to Taylor Swift concert, mailed ambassador desk for guaranteed room and got following reply:

"Welcome back and Thank you for choosing IHG Hotels & Resorts for your upcoming travel plans on May 23, 2024. I truly appreciate your continued loyalty as a Diamond Ambassador member.

Regarding your request for accommodation from May 23 to May 26, 2024, both of your preferred hotels are currently sold out. However, I reached out to both properties for Guaranteed Room Availability, and I'm pleased to inform you that the Holiday Inn Lissabon - Continental has responded positively to our request.

I spoke with Paolo, the Front Office Supervisor, who provided a rate of 342 EUR per night. The estimated total for a three-night stay, including taxes, would be 1037.60 EUR.

If this rate meets your approval, please let us know, and we will be happy to endorse you to the hotel for further assistance under the Guaranteed Room Availability.
"

We made use of it and had a great stay. So really happy how IHG handled this.