Ah. Now I understand. You have a literal "\n", not a newline in your data, but you don't want to capture that. The easiest way is to restrict the character class to not include the backslash:

for (<DATA>) {
    print "Matched: $1\n"
        if /DIP\s+\S+\s+([^\\\s]+).*?\\n/;
    
};
__DATA__
*** ALARM 009 A2/APT \"KEN5-132/019/00\" 100831   1511      \nSWITCHIN
+G NETWORK TERMINAL FAULT\n\nSNT                TCASE  STATE    FCODE 
+SUBSNT  INFO        DIP amad theoneiwant\n RTDMA-63           4      
+BLOC     38\n\nEXTERNAL EQUIPMENT FAILURE\n\nEXTP                MG\n
+2-2-010109          MEAPH\nEND
*** ALARM 009 A2/APT \"KEN5-132/019/00\" 100831   1511      \nSWITCHIN
+G NETWORK TERMINAL FAULT\n\nSNT                TCASE  STATE    FCODE 
+SUBSNT  INFO        DIP amad theoneiwant      \n RTDMA-63           4
+      BLOC     38\n\nEXTERNAL EQUIPMENT FAILURE\n\nEXTP              
+  MG\n2-2-010109          MEAPH\nEND
*** ALARM 009 A2/APT \"KEN5-132/019/00\" 100831   1511      \nSWITCHIN
+G NETWORK TERMINAL FAULT\n\nSNT                TCASE  STATE    FCODE 
+SUBSNT  INFO        DIP amad theoneiwant hello world \n RTDMA-63     
+      4      BLOC     38\n\nEXTERNAL EQUIPMENT FAILURE\n\nEXTP       
+         MG\n2-2-010109          MEAPH\nEND
*** ALARM 009 A2/APT \"KEN5-132/019/00\" 100831   1511      \nSWITCHIN
+G NETWORK TERMINAL FAULT\n\nSNT                TCASE  STATE    FCODE 
+SUBSNT  INFO        DIP amad theoneiwant\n RTDMA-63           4      
+BLOC     38\n\nEXTERNAL EQUIPMENT FAILURE\n\nEXTP                MG\n
+2-2-010109          MEAPH\nEND
[download]

The character class \S will not match any whitespace, but the character sequence "\n" (that is, backslash, followed by "n") is not whitespace.

A better way would be to decode the lines, i.e. convert the "\n" into newlines.

while (<DATA>) {
    s/\\n/\n/g;
    print "Matched: $1\n"
        if /DIP\s+\S+\s+(\S+).*?\n/;
    
}
[download]

Holy cow. Thank you. I've spent over 3 hours trying to tackel it! Thank you!

Corion's analysis is right. As a question, you may not even need to fiddle with the \n at all, by changing from \S to \w. a word char is 0-9A-Za-z_ and therefore \ won't match. Its not clear to me what all kind of characters could be in "theoneiwant" anyway if your data allows it something even simpler can be done...

for (<DATA>) {
   print "Matched: $1\n"
            if m/DIP\s+\S+\s+(\w+)/;     #([\w-]+) to allow -   
};
[download]