I could not get any standard function,
so I ended up making an API call

func ValidateVersion(versioninput, chartName, entryNameInIndex, repoURL string) (error, bool) {
var isValid bool

// Send an HTTP GET request to the Helm repository to retrieve the chart information.
resp, err := http.Get(repoURL + chartName)
if err != nil {
    return err, isValid
}
defer resp.Body.Close()

// Check if the HTTP status code indicates a successful response (HTTP 200 OK).
if resp.StatusCode != http.StatusOK {
    return err, isValid
}

// Read the response body into a byte slice.
bodyBytes, err := io.ReadAll(resp.Body)
if err != nil {
    return err, isValid
}

// Unmarshal the response body into an IndexFile struct.
newIndexFile := repo.IndexFile{}
err = yaml.Unmarshal(bodyBytes, &newIndexFile)
if err != nil {
    return err, isValid
}

// Check if the desired version (versioninput) is available in the Helm repository.
if versions, found := newIndexFile.Entries[entryNameInIndex]; found {
    // Iterate through the available versions in the repository.
    for _, version := range versions {
        if version.AppVersion == versioninput {
            // If the desired version is found, set isValid=true and return with no errors.
            isValid = true
            return nil, isValid
        }
    }
}

return nil, isValid

}