I have analyzed you issue and came to the following conclusions:

1. The Ingress will work and these Warnings you see are just to inform you about the available api versioning. You don't have to worry about this. I've seen the same Warnings:

@microk8s:~$ kubectl describe ing
Warning: extensions/v1beta1 Ingress is deprecated in v1.14+, unavailable in v1.22+; use networking.k8s.io/v1 Ingress

2. As for the "why" this is happening even when you use apiVersion: networking.k8s.io/v1, I have found the following explanation:

This is working as expected. When you create an ingress object, it can be read via any version (the server handles converting into the requested version). kubectl get ingress is an ambiguous request, since it does not indicate what version is desired to be read.

When an ambiguous request is made, kubectl searches the discovery docs returned by the server to find the first group/version that contains the specified resource.

For compatibility reasons, extensions/v1beta1 has historically been preferred over all other api versions. Now that ingress is the only resource remaining in that group, and is deprecated and has a GA replacement, 1.20 will drop it in priority so that kubectl get ingress would read from networking.k8s.io/v1, but a 1.19 server will still follow the historical priority.

If you want to read a specific version, you can qualify the get request (like kubectl get ingresses.v1.networking.k8s.io ...) or can pass in a manifest file to request the same version specified in the file (kubectl get -f ing.yaml -o yaml)

Long story short: despite the fact of using the proper apiVersion, the deprecated one is still being seen as the the default one and thus generating the Warning you experience.

I also see that changes are still being made recently so I assume that it is still being worked on.