I have just installed the Octopus.Tentacle.6.1.736-x64.msi on our 3 x AWS EC2 instances. They are all running Windows Server 2019 (Builds 17763.1158 and 17763.2061)
Even though this is the latest Tentacle download from the Cloud management console, the Deployment Targets page shows the message “Upgrade available” next to each of these targets. I selected “Update Calamari on Deployment Targets” from the ellipsis menu anyway and got a tick next to each target so it seems to have successfully upgraded them. However the “Upgrade available” message remains.