Thank you @threadi – that was the solution. ??
Installed Yoast, ticket a single checkbox (Show categories in search results) and verified with curl on the category-page and the individual url:
<meta name='robots' content='noindex, follow' />
<meta name='robots' content='index, follow, max-image-preview:large, max-snippet:-1, max-video-preview:-1' />
Thank you again ??
