This problem occurred on mac OS 10.15: after some hours of normal activity, it is no longer possible to launch the NoMachine client and the following error is issued: 

the error message.

dyld: Library not loaded: @loader_path/../Frameworks/lib/libmdnsd.dylib
  Referenced from: /Applications/NoMachine.app/Contents/MacOS/nxplayer
  Reason: no suitable image found. [...]	
	file system relative paths not allowed in hardened programs
[...]

Problem is triggered by missing entitlement for NoMachine.app:

com.apple.security.cs.allow-dyld-environment-variables