I've rebooted the host after the upgrade.
I just rebooted the machine again:
root@srv-eg-beta3:~# uname -r
5.0.21-5-pve
root@srv-eg-beta3:~#
I use one onboard nic (intel - asus board) and an additional external (PCI-Slot) NIC, because it wasn't working with the onboard nics - but the result...