I have 2 VMs set up in Azure -- one hosting ArcGIS Server 10.8, and the other hosting ArcGIS Web Adaptor 10.8.
I was able to configure ArcGIS Web Adaptor for ArcGIS Server using HTTPS. Now, I want to configure it using HTTP (to access ArcGIS Server at http:<internal DNS name>:6080/arcgis). However, it seems that Web Adaptor is still trying to force the connection to use HTTPS.
When I tried to configure the web adaptor using the web interface, and click to configure a GIS server:

the browser is directed to https
/webadaptorhost/server/webadaptor/server:

If I manually change it to use http, I get to the configuration page. When I try to configure the web adaptor

I get the following error message:

If I try to configure the web adaptor using the ConfigureWebAdaptor utility, it looks like it's trying to force HTTPS

Port 6080 is open on the Server machine.