I think this could be the answer : https://serverfault.com/questions/648262/filesmatch-configuration-to-restrict-file-extensions-served

It says that the FileMatch is before the DirectoryIndex so you have to add your root to the allowed strings

<FilesMatch "(^$)|^.*\.(css|html?|js|pdf|txt|gif|ico|jpe?g|png|pl|php|json|woff|woff2|eot|svg|map)$">