You can read a rather entertaining text by trying to run Network Utility in MacOS Big Sur.
To access network tools (netstat, ping, lookup, traceroute, whois, finger), open Terminal and enter the command indicated below on the command line.
If you have problems with Wi ‑ Fi, open Wireless Diagnostics and follow the on-screen instructions to analyze your network connection.
Just in case, which means each command:
▪️ Netstat : checking computer routing tables by looking at a detailed summary of the types of packets sent and received using common network protocols.
▪️ Ping : check the connection of the computer with the computer or other device at the specified network address.
▪️ Lookup : View information provided by a domain name server (DNS).
▪️ Traceroute : Tracing the message path over the network from computer to computer.
▪️ Whois : Receive from the whois server information about the ownership of the specified domain name.
▪️ Finger: use the Finger protocol to obtain information about the user at the specified user name and domain address.
▪️ Port Scan : Scan open TCP ports at a specified Internet or IP address.
In other words, the operating system no longer has this program. All diagnostic actions are carried out through the Terminal . Just enter commands and look at the result.