I use helm 3

helm search repo --regexp "chartmuseum/my-app" -l

and get result

    NAME                            CHART VERSION   APP VERSION     DESCRIPTION                
chartmuseum/my-app                  1.2            1.16.0          A Helm chart for Kubernetes
chartmuseum/my-app                  1.3            1.16.1          A Helm chart for Kubernetes

I want find latest 1.16.* APP VERSION with --regexp flag

helm search repo -l --regexp '1.16'
   No results found

Looks like regexp use only NAME column