The AJA Io 4K Plus is supported compatible with just:in mac v.5.5, but it only with supports SD and HD video modes. UHD recording (, one UHD channel via a 12G input) , will be supported with v.6.0.
The Due to hardware limitations, the AJA Io 4K Plus only supports only one a single dedicated 12G input or 12G output channel, due to hardware limitations.