In the actual Azure subscription you just need to create an Azure Container Registry resource to host the image. I believe you can also use Docker Hub, if you prefer.
That should be about it. The effect of this is to "zip up" your loose 'js' files (or whatever), making deployments much faster. The build happens before this step, so the container image is "final" and will run directly without needing any npm steps or whatever at deployment time.
If you need something like hot-reload or similar very fast deployment times, then App Service is probably not the right environment for you. However, with containers its often possible to have a fast local deployment edit-build-test loop and then have the same environment running in production. This is the main benefit of containers!
Sorry but I don't want to install Microsoft's text editor to deploy an app.
It's a basic next.js app, nothing special.
I tried the app service config on GitHub actions and it was ridiculous to say the least. 15 minutes to copy the files over and then it didn't launch the app correctly even after I specified how to launch it. Pitfalls at every step.
It's like the UI was designed by a child.
You're saying a lot of "just", and to be honest those tasks aren't simple things that I can just do. For example having a docker registry that I now have to secure and babysit is not what I'm here for.
I'm not sure why you're trying to argue that Azure is good.
App Service can run containerised workloads just fine.