@Marek , For the error, based on my research, this can occur if the account specified in the registry for the server setup value below does not exist as a valid account. This is likely due to the fact that it was removed in the past.
HKLM\Software\Microsoft\Microsoft System Center Virtual Machine manager Server\Setup\VMMerviceAccount
here is a link for the reference:
https://social.technet.microsoft.com/Forums/en-US/7e66f834-bff2-43f1-99e4-d8b746d20f00/error-2912-when-adding-hyperv-host-within-vmm?forum=virtualmachingmgrhyperv
We can check the account. to see if it can be fixed If there's any update, feel free to let us know.
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