Hi,
You need to select a VM size that supports Confidential compute. For example, DC* or EC* sizes. Please click on the See all sizes link and then select a VM size that has "Confidential compute" in the Type column.
Please note you need to have available Quota for the specific VM size that you need. After you click on See all sizes link if no sizes show available, try clicking on Insufficient quota - family limit. From there you may choose which size you want and click the Request quota link to request a quota increase.
Once your quota increase is approved you can start the Create a virtual machine process again and select the size that you just got approved.
Please click Accept Answer if the above was useful. If you still assistance or something is unclear add a comment.
Thanks.
-TP