This is NOT about helm, but cPanel, my mistake.

I tried in on the demo en searched in the manual, buty I cannot find an answer.

Is in in the cPanel possible to use wildcard subdomains on vhost level (not dns).
You will get somethin like:
domain.tld --> /dir/domain.tld/public_html/
www.domain.tld --> /dir/domain.tld/public_html/
*.domain.tld --> /dir/domain.tld/public_html/