I am up against the same issue. I need to read and write serial data plus control RTS and DTR lines to write to the flash memory of a processor on a proprietary device. The "open(fd,flags)" function fails when sandbox is enabled. It works properly when sandbox is disabled. Without sandbox, it appears that I cannot validate the app. I am in the middle of a Catch-22

I've run into a similar problem. I am developing an app which will flash the memory of a device which I designed through the usbserial driver. I can see the device as a usbserial device in the system report. I can retrieve the device name and display it as a choice (the only choice in this case) of an available port. When I try to open the port, the app fails. When I disable SandBox, the port opens properly and the flash operation continues as expected. OS 13.4 XCode 14.3.1