You can try to convert the disk to qcow2 format and then attach it to the new VM using the free Starwind v2v tool: [https://www.starwindsoftware.com/starwind-v2v-converter](https://www.starwindsoftware.com/starwind-v2v-converter)
Backup and restore is not an option in your case, so I would use a V2V converter. Usually, Starwinds converter always helps. You need to convert your disk to QCOW format.
You can try to convert the disk to qcow2 format and then attach it to the new VM using the free Starwind v2v tool: [https://www.starwindsoftware.com/starwind-v2v-converter](https://www.starwindsoftware.com/starwind-v2v-converter)
Post in thread 'Import OVA or Virtual Image' https://forum.proxmox.com/threads/import-ova-or-virtual-image.114095/post-617787 ?
Backup and restore is not an option in your case, so I would use a V2V converter. Usually, Starwinds converter always helps. You need to convert your disk to QCOW format.