Rhino 5.5.4 Bug: Material Editor

I’m getting a total freeze when trying to open Material Editor on Rhino 5.5.4. Is this version still supported?

Mac OS 10.14.6 (18G95)
MacBook Pro (13-inch, 2017, Four Thunderbolt 3 Ports)
Processor: 3.1 GHz Intel Core i5
Memory: 16 GB