Is it possible to install Windows Server 2019 Standard in Azure?
Solution 1:
No, you can only install Data Centre. There should be no need for installing another version.
Solution 2:
I agree that there is no real reason to install Standard vs Datacenter and all images from Azure use the Datacenter edtion.
That said, you can always create and upload your own images with whatever you want on them, its a lot of work and I would not recommend it but its technically possible.