I installed Windows Server 2019 Standard (German edition) on PVE 7.2-3 inside of a i440fx-6.2 virtual machine and got a nic working.
During the Windows Server setup procedure there was no nic present.
After setup I mounted the virtio-win drivers (version 0.1.215) and installed virtio-win-gt-x64.msi to make sure I got most of the drivers.
I then shut down the vm to add a virtio nic to it and booted it up again.
The nic was present in the device manager but faulty (yellow icon, you know the drill).
Here another reboot was required. Took a little while longer but don't worry, it'll be fine.
I selected the nic in the device manager and updated the driver by manually setting it to "[my iso mount point]\NetKVM\2k19\amd64".
Windows tried to tell me it was already using the best driver for this device so I selected it again and "uninstalled the device".
After scanning for new hardware (magnifier on monitor icon inside the device manager's navbar) the nic showed up again without any problems.
From that point on even after unmounting the drivers iso and multiple reboots, the nic keeps working.
I also tried that whole process using version 0.1.217 of the virtio-win drivers but it didn't work. Not even virtio-win-gt-x64.msi ran without problems.