How to generate a locally unique identifier LUID using php

/**
* Returns a string that is unique in the local system.
* Returns a 32-character string in the form of '7dac352074f221f3edc74d265c65a636', or 'd198d8fc56ffed627f3f8313d6f06acf'
*/
function LUID(){
return MD5(microtime());
}
?>

In fact, just One line: return MD5(microtime());

Logically, the string returned by microtime() is already unique. After testing, even if microtime() is executed continuously, the return value will have a difference of more than 100us. When the user clicks, it will be transmitted on the network and then sent to the server. The processing interval is much more than a few tens of ms, and adding md5 will only complicate the results.