pass: 311138
The keygen was published for burpsuite 2.1.04 pro.
To run it, java 1.8.0_221 is required, because of which TLS 1.3 interception will not be available, otherwise the keygen is working fine.
run:
java -noverify -Xbootclasspath/p:burp-loader-keygen-2_1_04.jar -jar burpsuite_pro_v2.1.04.jar
or from keygen itself