@Montypython
You've also mentioned "VM Server", though I'm not clear if that means you upgraded the hypervisor or guest (I'll assume it's the latter.)
With a virtual guest, you usually need to select a guest profile that matches the guest operating system, and there's a good chance given the age difference between 2012 R2 and 2019 that your profile isn't suited to Server 2019.
Secondly - and this only really applies if you sort out the first issue above, you should consider uninstalling (if the old ones are still present) and re-installing your hypervisor's integration tool extensions. You might find they're either missing completely or profoundly out-of-date.
But as Dave said, check with your vendor - irrespective of whether that's for hardware or a hypervisor.
In-place upgrades frequently come with a high troubleshooting cost. My personal recommendation is steer clear of them.
Cheers,
Lain
