when i have images in a custom registry i have to tag the image and also refer to this custom repo in my yaml files for instance image: 172.16.0.2:5000/myapp:0.3 is there a way to not specify the registry server and k3s by default looks to that address? so it becomes image: myapp:0.3

Not sure if it is what you meant, but you can create a secret that holds your dockerhub account information and pull that secret within your yaml. After which you can just call your image(s) directly, as shown in the example below.

@chilly-telephone-51989 Yes, you can. Have a look at this https://rancher.com/docs/k3s/latest/en/installation/private-registry/ or this https://docs.rke2.io/install/containerd_registry_configuration/. What you want to achieve is configured in containerd