I have seen requests to get a working MultiWiiConf on a more recent macos. I just had to do a rebuild myself.
a) get or update appropriate driver for the usb-serial interface - good verification is to build and upload MultiWii 2.4 to the FC with the arduino IDE app.
b) get MultiWiiConf.pde (the source) from github
c) get or reinstall Processing.app 2.2.1 - it is ancient but good enough
d) get and install library controlP5 2.0.4 - it is ancient but just right for this source
dd) on win10 install /downgrade to Java version 8 (hints to bypass oracle can be found on github) - it was not neccessary on my macos instance
e) compile and run MultiWiiConf.pde in Processing.app - if it lists the usb-serial interface and you can connect, then you are good.
f) export as MultiWiiConf.app from Processing.app to have a standalone app for future use.
last step f) did not work for me on win10 but step e) is good enough for the few occasions