A few years ago, there were 3 tools for diagnosing network problems: Network Utility (gone in Big Sur), Wireless Diagnostics, and Network Diagnostics (also gone). And what can networkQuality tell you about Private Relay?
WhatRoute
You might be lucky and solve it by inspiration. When that fails, fall back on a careful, thorough and systematic approach as explained here.
With more and more of our documents cloudbound, failure of an Internet connection can spell disaster. Do you give up and chat, read a book, or what?
The Eclectic Light Company 