Using Juce 6.1.2, the Add new resource button crashes Projucer.
It would likely be helpful if you could run the Projucer in the debugger and report the location of the crash, and stack trace.
In addition to what @cpr2323 said, the Projucer tries to show a preview, so it might be of interest what kind of file you were adding.
Here is what I see in Xcode 11.3.1 in debug mode (see image below).
To reproduce the issue : create a new plugin, a new GUI component, go to the Resources tab, click the Add new resource button, choose a jpg or png. In my case it crashes (even with the portmeirion.jpg file from the Juce Assets).
wow… that is in osx code! hopefully a mac person can shed some light. 
same problem here. Any fix in the horizon?
I’ve pushed a fix for this to the develop branch here:
that worked, thanks!