Third-party vendor that builds some widely used NetSuite SuiteApps are telling me that the message in the Chrome console is something that we have done on our instance of NetSuite??? Has anyone ever seen this?

not really netsuite instance. You are very likely working with a company that has an IT team that has actually setup a chrome policy to block dev tools on netsuite

Exactly what I told them - not sure why their technical support team want to say this is a NetSuite issue bearing in mind these guys build SuiteApps.

Have seen this before when your browser is logged in using a corporate account. The admins of "Googles" at the workplace can actual block devtools via configuration. Fun times and it will be what @battk mentioned. They might not even know that they blocked them. Try Edge instead (before you yell, MS Edge is also Chromium based so there is a method to my madness 🙂 )