One thing you can check is to see whether there are updated drivers for that device. Now, how do you have the CAT control configured for Fldigi/Flrig? A USB-Serial cable or something similar? Odds are the driver didn't load.
It has nothing else to do with Flrig/Fldigi not talking to your TS570D. You should select USB Audio Codec in your soundcard setup in Fldigi in order to use it.
You may have to 'reauthorize' the apps to run with the Gatekeeper protection in place (go to Applications, right click on the Fldigi app, and select 'Open'. Click to expand.Both Fldigi and Flrig work just fine with High Sierra.
