Thanks for your help! Unfortunately that didn't work, both keys aren't accepted by my Windows Server 2019 Standard :-(
No need for google/external links IF that is the case: https://forums.mydigitallife.net/threads/windows-server-2019-activation.79812/page-2#post-1553794
CSVLK? You want to activate it with Volume_GVLK key? or with Volume_CSVLK key to be KMS Activation Server for Client?
I want to activate it with the KMS_VL_ALL tool. I have installed the server using the retail ISO afaik.