Sorry I thought that you were talking about the Nitropad, my bad (which is why I answered because I checked for x230 which is what the NitroPad is).
sudo cpu-microcode-info on dom0 will tell you if microcode is available/installed.
Providing the output here would permit others to jump in as well.
I would advise to ask for Nitrokey to come here and reply to all so that they do not have to reply to each individual questions going their way.
The same advice as in my other post will also share the same light on what mitigations are applied from Xen and kernel for your CPU:
Where
Was right on point and permits you to get to kernel report on the current vuls/mitigations applied.