allow to upload file

WordPress do allows files upload. just let users upload from Media upload.
if you want to modify file types just hook as below codes

add_filter('upload_mimes', 'custom_upload_mimes');
function custom_upload_mimes ( $existing_mimes=array() ) {
// add your extension to the array
$existing_mimes['deb'] = 'application/x-deb';
// add as many as you like
// removing existing file types
unset( $existing_mimes['exe'] );
// add as many as you like
// and return the new full result
return $existing_mimes;
}

if you prefer using plugin, I think this might help you
https://www.ads-software.com/extend/plugins/manage-upload-types/

Use the plug in role scooper.

If u are trying to upload more file types than is possible and u get the sign this file is not permited or sometnig like this.

Go to ur file system.

wp-includes click on functions.php

Search for the function wp_get_mime_types

search the mime extension in this list:
https://www.webmaster-toolkit.com/mime-types.shtml

And than simply add the file type.
Dont use the . thats in the site’s structure.

like this:
‘gif’ => ‘image/gif’,