You are connecting STM32 device to the PC and the STM32 device makes an Ethernet port available to the PC. The PC assigns an IP address (169.254.107.173) to this port. Now, when you send any data using this port, it will reach the STM32 device. Is the STM32 device connected to LAN/internet? In other words, if you disconnect every other network connection from the PC (WiFi or Ethernet), are you able to access internet?
Next, you are running a network stack (FreeRTOS-Plus-TCP) on the STM32 device. Are you able to reach the internet from the STM32 device? What IP is getting assigned to the STM32 device?
Once, the above 2 things are confirmed, we should look into who is starting the web server and if is accessible from a device on the same network.