Hello Szunomar P,
Had exact same issue.
Resolved it by using the KMS Client Setup Key during upgrade.
KMS client setup keys
Specifically this one:
Windows Server 2019 Datacenter WMDGN-G9PQG-XVVXX-R3X43-63DFG
On the other hand In-Place Upgrade is not a great idea. Microsoft does not support In-Place Upgrade and must be a good reason with that. The best practice, specially in the case of HyperV Hosts is to migrate the VMs from host to host:
-Shut down VMs
-Merge any checkpoints
-Export VMs to shared drive on new hardware
-Import into new host
-Update Hyper-V services on VMs
-Boot App server and test before booting AD
-Decommission old hardware
Hope it helps you!
Do not forget to vote if helpful or mark as an answer if it resolved your query!
Best regards!
Luis P