What does the link symbol mean in the Wi-Fi network list on iOS? What does the "link" () mean in the Wi-Fi network list on iOS?

Example (see red rectangle):
It means it's not a regular WiFi, it's a computer-to-computer network. In this case, it means that your the Wifi network host is an iPhone sharing itself as a Hotspot and other properties may be available.
See also this Apple Support article.

For personal hotspot on iPhone 8 or earlier, you can also see how many devices joined your Hotspot.