Checking files on the server at boot?

Question

PHP

Question 1.
I check the uploaded files to the server like this:

$finfo 	= finfo_open(FILEINFO_MIME_TYPE); 
$mime 	= finfo_file($finfo, $file);
finfo_close($finfo);

Is this enough, or do I need to install an antivirus on the server?
Question 2.
Found mime file types.

$mime_types = array(
            'txt' => 'text/plain',
            'htm' => 'text/html',
            'html' => 'text/html',
            'xml' => 'application/xml',
      
            // images
            'png' => 'image/png',
            'jpe' => 'image/jpeg',
            'jpeg' => 'image/jpeg',
            'jpg' => 'image/jpeg',
            'gif' => 'image/gif',
            'bmp' => 'image/bmp',

            // archives
            'zip' => 'application/zip',
            'rar' => 'application/x-rar-compressed',

            // audio/video
            'mp3' => 'audio/mpeg',

            // adobe
            'pdf' => 'application/pdf',
            'psd' => 'image/vnd.adobe.photoshop',
            'ai' => 'application/postscript',
            'eps' => 'application/postscript',
            'ps' => 'application/postscript',

            // ms office
            'doc' => 'application/msword',
            'docx'=> 'application/vnd.openxmlformats-officedocument.wordprocessingml.document',
            'rtf' => 'application/rtf',
            'xls' => 'application/vnd.ms-excel',
            'xlsx'=> 'application/vnd.openxmlformats-officedocument.spreadsheetml.sheet',
            'ppt' => 'application/vnd.ms-powerpoint',
            'pptx'=> 'application/vnd.openxmlformats-officedocument.presentationml.presentation',

            // open office
            'odt' => 'application/vnd.oasis.opendocument.text',
            'ods' => 'application/vnd.oasis.opendocument.spreadsheet'
        );

But for some reason finfo_file($finfo, $file); produces different mime types for some files, for example txt files. What does it depend on?
The main question.
How to check files uploaded to the server by users?