i will communicate over GRPC with an application that is installed on a Windows 2016 Sevrer.
The problem is, my Node-Red use TLS 1.3 and the App on the Windows Machine can only communicate over TLS 1.2.
How can i config my FLOW to communicta over TLS1.2
Well, first question would be why are both devices limited to a single TLS version as that isn't a good setup at all. Clients and servers should be able to use multiple versions with only old versions prevented. So that indicates to me that your TLS config isn't quite right. This is important because TLS, like all PKI based systems is prone to config errors making things insecure.
If you, for some reason, can't fix that. Then one approach would be to set up an intermediary system with the correct TLS config. That could be another Node-RED instance of course.