It is possible to create a white list; however, it might not work if you are currently blocking all the traffic to the internet.
Below you can find more information related to this function:
Based on your comments, here are some suggested options that might work for you:
1. You could specify the server IP address on the traffic rule. (Through a nslookup command in the CMD, you can get this IP address).
2. Let the LAN-Connected devices reach any server listening to a specific port. (Your current solution)
3. Combining the options above.
However, it seems that the last two questions are no longer inside the initial query scenario. Therefore, following the forum best practices, I will kindly ask you to submit another query for these upcoming questions regarding Traffic rule configuration since your initial query subject is no longer the issue.