I belatedly got around to updating my copy of launch4j on macOS from the 3.14 I've used for ages to the 3.50 release. I ran into two problems. They were easily enough fixed, but I'm posting here so that other can learn from my experiene whether or not these are things that the author can fix.
First, in the top level of the launch4j distro is a shell script titled launch4j. My copy of macOS very much dis-liked the end-of-line characters in the file, complaining that it couldn't find "#!/bin/sh^m". I've had a tool around for literally decades to flip the EOL chars in a file, so I ran that, and the script is now fine. This seems like something the author could correct in the launch4j distro.
Next is that the Gatekeeper security software doesn't like the codesigning (or lack thereof) of the two binaries in launch4j's bin directory, so you need to somehow mark them as being kosher. I ended up using Terminal.app to cd into this directory and then executed the commands
xattr -d com.apple.quarantine windres
xattr -d com.apple.quarantine ld
Having done the above, I found I had to change exactly one line in an app's launch4j.xml file to make it "3.50 compatible". A few minutes later I was able to run the app in Windows via Parallels
Adding that I ran into the problem with windres and ld before as described in #215, but control-click to manage the permissions, but that doesn't work with the Sonoma M1 Mac I'm now using.
Cripes, one more thing. After fixing the EOL characters on the top-level launch4j shell script, don't forget to turn the execute permissions back on.