There’s still a way to do it but it’s convoluted compared to if they’d just add a damn resource monitor into the game itself.
If you still care about figuring out your ping: this comment on reddit from a year ago tells you how to find your games server IP, from there you can just fire up command prompt and hit with
ping -n 100 <IP/Adress>
This should return your ping and packet loss with the server.
Scrolling through servers on CS:Source trying to find one that wasn’t pinging harder than my anxiety… Those were the days.