To be honest, I am not familiar with this Htaccess 301 Redirect Rules but you can give it a try this.

RedirectMatch 301 /articles/(.*)\?format=amp /articles/$1

However, I am really sorry but unfortunately this is beyond the scope of our support.

Thanks for understanding.

No problem Arlex.

I've found a solution :

RewriteCond %{QUERY_STRING} "format=amp"

RewriteRule (.*) /$1? [R=301,L]

It might be useful for other users

Philippe

Thanks for sharing.