Hi md5hash,
Although there is no official Microsoft document to announce that Volume Licensed Office 2019 is forever stuck at Version 1808, I am afraid, it is the truth.
Here is a similar thread "Office 2019 (Volume licensed Versions) will be Version 1808 forever".
(Please Note: Since the web site is not hosted by Microsoft, the link may change without notice. Microsoft does not guarantee the accuracy of this information.)