Hi Olivier Fermy,
I understand that you are facing issue when trying to capture an image of your Trusted Launch virtual machine with an error "Virtual machine doesn't match the Security type of this VM image definition - Security type: Trusted launch supported". This message says that your Virtual machine is not "Trusted launch**"** security type.
As said, the option "Trusted launch supported" works only if the VM does not contain VM Guest State Information. If your VM contains VM Guest State Information, then we need to use the "Trusted Launch".
Please check in the portal under Overview tab about your VM security type. If it is not "Trusted Launch" VM, then you can enable trusted launch on an existing-vm
As you have mentioned, you have tried with B-series, D-series V5 but Dpsv5-series, Dpdsv5-series, Dplsv5-series, Dpldsv5-series are not currently supported size families.
Please check the document about the Trusted Launch for Azure virtual machines
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Thank you.