* VMSS1 -Yes
Standard Windows virtual machine platform images are supported.
Flexible orchestration mode is supported.
Note: Enabling Automatic Guest Patching on single-instance VMs or Virtual Machine Scale Sets in Flexible orchestration mode allows the Azure platform to update your fleet in phases.
* VMSS2 - No
Custom images are not supported.
* VMSS3 - Yes
Standard Linux virtual machine platform images are supported.
Flexible orchestration mode is supported.
* VMSS4 - No
Custom images are not supported.
Note:
Automatic VM guest patching, on-demand patch assessment and on-demand patch installation are supported only on VMs created from images with the exact combination of publisher, offer and sku from the below supported OS images list. Custom images or any other publisher, offer, sku combinations aren't supported. More images are added periodically.
Reference:
https://learn.microsoft.com/en-us/azure/virtual-machines/automatic-vm-guest-patching