Since PHP 7.4 is very different from 7.3, there are some problems.
According to PHP Manual (https://www.php.net/manual/en/migration74.other-changes.php),
The bundled libsqlite has been removed. To build the SQLite3 extension a system libsqlite3 ≥ 3.7.4 is now required. To build the PDO_SQLite extension a system libsqlite3 ≥ 3.5.0 is now required.
A site suggested me to solve this problem by copying "libsqlite3.dll" from "C:\xampp\php" and paste it to "C:\xampp\apache\bin" and it worked.