I have created a .net 2.1 core mvc and now ready to host it on Azure WebApp. I am yet to finalize logging.
https://stackify.com/azure-app-service-log-files/
I read above link and found the below snapshot to configure Application logging and Web Server logging.
however in my WebApp all I can see is:
Is this due to my app service plan? How do I configure Application logging and Web server logging?
Yes, it's due to the app service plan. Just check the app on a basic Linux service plan on my side. It's the same as you. Once you click the Application Logging(filesystem) on, (This setting turns itself off after 12 hours), then save it and go back another page or refresh the current page, you will see the web server logging. Also, I found this UI always jumps to the previous page like you(without web server logging), after a while, you click another page, this will jump back.
Moreover, you could check the Log Stream to have the ability to see logging information in real-time (or as close to it as possible). Refer to the blog about Azure Tips and Tricks Part 30 - Working with Log Stream and Azure App Services.
It's likely a UI bug in the Azure portal. If you want to improve this, you could request feedback.