It's been several years since I worked with one of those. But I think the ethernet module is Port 2 and Port 1 is still available when you add it. The following is from GFK-1645M, page 117:
Port 1 is a built-in RS-232 serial port with an RJ-45 connector.
A second port can be added to a 40-Point Micro PLC using one of the port Option Modules described in Chapter 14:. If a second port is installed, both ports can be used for programming. Only one port can be used at a time for programming, but both ports can be used for monitoring at the same time.
But, if it was working OK on a different computer, then it seems the problem is in the way the new computer is set up. Is Machine Edition trying to use Wi-Fi instead of the hardwired ethernet port? Is the ethernet port you're using on the computer set up for fixed IP address and have you set it to be in the same subnet as the PLC? Is your version of Machine Edition compatible with the OS you're using in the new computer? You previously needed version 9.5 for Windows 10 compatibility. I don't know what version you need for Windows 11.