If my understanding is correct, you can't create new legacy mode with latest pan-os.
If you need lagacy mode environment, I believe you need to prepare very old image with lagacy mode and then keep upgrading it 'til the latest. https://docs.paloaltonetworks.com/panorama/11-1/panorama-admin/panorama-overview/panorama-models
Legacy mode ( ESXi and vCloud Air only )—In this mode, the Panorama virtual appliance receives and stores firewall logs without using a local Log Collector (see Deploy Panorama Virtual Appliances in Legacy Mode with Local Log Collection). By default, the virtual appliance in Legacy mode has one disk partition for all data. Approximately 11GB of the partition is allocated to log storage. If you need more local log storage, you can add one virtual disk of up to 8TB on ESXi 5.5 and later versions or on vCloud Air. Earlier ESXi versions support one virtual disk of up to 2TB. If you need more than 8TB, you can mount the virtual appliance in Legacy mode to an NFS datastore but only on the ESXi server, not in vCloud Air. This mode is only available if your Panorama virtual appliance is in Legacy mode on upgrade to PAN-OS 10.0. On upgrade to PAN-OS 9.0 and later releases, Legacy mode is no longer available if you change to any other mode. If you change your Panorama virtual appliance from Legacy mode to one of the available modes, you will no longer be able to change back into Legacy mode.
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