Hello,
The intranet shared folder is implemented using the SMB protocol, which requires TCP port 445 to transmit data. If you want to access the intranet shared folder through the Internet, you need to set up port mapping on the router and map a port on the Internet to port 445 on the intranet. I recommend that the port mapped on the public network be in the range of 1024 to 65535. In this method, you need to make sure that your router supports port mapping and that your external IP address is fixed.
Best Regards
Zunhui