Answer

1. Open the Required Port in the Firewall:
   In my case, the problem was that Ubuntu's firewall (ufw) was blocking traffic on port 5000. You can allow this traffic by running:

   sudo ufw allow 5000
   

   This should open the port for external connections, allowing the macOS container to access usbfluxd on the host.

2. Restart usbfluxd on macos (if necessary):
   After updating the firewall, restart usbfluxd to ensure the changes take effect.