- If you consider that all the steps are being performed on the portal, there is no "Allow Gateway Transit" to be "Selected" as described in the article below:
https://learn.microsoft.com/en-us/azure/vpn-gateway/vpn-gateway-peering-gateway-transit#to-add-a-peering-and-enable-transit
- If you consider all the steps are being performed in PowerShell, using "Add-AzVirtualNetworkPeering" command, so, you have the attribute "-AllowGatewayTransit" to be "Set" not "Selected", since its a boolean option.
https://learn.microsoft.com/en-us/azure/vpn-gateway/vpn-gateway-peering-gateway-transit#ps-same