RedirectMatch how to match any words but not index and nothing

You may add a new rule below your existing rule:

RewriteCond %{THE_REQUEST} \s(/folder/[\w-]+)\.php[?\s] [NC]
RewriteRule ^ %1/ [L,R=301]

THE_REQUEST matches only original URI sent by client, it won't match modified REQUEST_URI.

I found this question: Match everything except for specified strings that help me to fix regex.

RedirectMatch permanent /folder/(?!.*(index))(.*)\.php https://www.site.it/folder/$2/

This rule match everything except index so redirect /folder/page.php only once to /folder/page/ but unfortunately, as @anubhava pointed out, this rule doesn't match any page name that contains index.

After further dig, I found this solution:

RedirectMatch permanent /folder/(?!index.php$|$)(([\w-]+)\.php$) https://www.site.it/folder/$2/

Anyway thanks to @anubhava that support me.