[I want to disable a specific day on calendar HELP]

I developed my own calendar and if I am understanding you correctly then you could do something like the following:

    protected function checkForEntry($calDate, $page = 'index.php') {
        
        $this->username = isset($_SESSION['user']) ? $_SESSION['user']->username : \NULL;

        $this->query = 'SELECT 1 FROM cms WHERE page=:page AND DATE_FORMAT(date_added, "%Y-%m-%d")=:date_added';

        $this->stmt = static::pdo()->prepare($this->query);

        $this->stmt->execute([':page' => $page, ':date_added' => $calDate]);

        $this->result = $this->stmt->fetch();

        /* If result is true there is data in day, otherwise no data */
        if ($this->result) {
            return \TRUE;
        } else {
            return \FALSE;
        }
    }

then simply disable the day though you don't have to use a database table to do this as I was just showing it's pretty simple. That is if I'm understanding correctly?