As a workaround, it is possible to convert the bootloader from incompatible GPT to MBR. It could be achieved via any liveCD, e.g. via Veeam Recovery Medea. The detailed procedure is outlined here. Thus, the idea is to restore the machine to Generation 1 first and then convert the bootloader to MBR – in this case, both requirements will be fit (G1 + MBR loader on BIOS).
Change of the environment from Hyper-V to physical machine or any other hypervisor that does not have such limitations if the scenario allows that.