How can I list only files that begin with "/LOG?"
Give a filename String to text...

String text = "/LOGsdfsdf";
if(text.startsWith("/LOG")){
//wee file begins with /LOG
}else{
// wops wrong file.
}


Look in here

https://www.arduino.cc/reference/en/language/variables/data-types/stringobject/

Method url startsWith("");

https://www.arduino.cc/reference/en/language/variables/data-types/string/functions/startswith