Hi Paul,
Thank you for reaching out to the Microsoft Q&A platform.
The Windows Server 2025 image you’re using doesn’t support VM Guest patching in selected region.
Not all regions currently support Windows Server 2025: Azure Edition images. If you try to use this feature in a region that doesn't currently support Windows Server 2025: Azure Edition, to work around this issue, use a different region that does currently support this feature, such as UK South, East Asia, or West Central US.
Source: https://learn.microsoft.com/en-us/windows-server/get-started/hotpatch#supported-platforms
Please find the supported images in below link for your reference:
If an answer has been helpful, please consider Accept the answer and "Upvote" to help increase visibility of this question for other members of the Microsoft Q&A community.
Thank you.