Here's my best reconstruction of what I did at the Terminal. I followed the basic instructions under the 'Reset the Network Configuration Files' heading of this article, but with some variations because I found some other junk in the same folder. (Based on my postmortem, this probably would have fixed the specific problem that I encountered.) Try the easy way first: under Prefs:Sharing:Internet Sharing, enable some sort of Internet sharing, e.g., Wifi to Bluetooth PAN.

(As it turns out, probably deleting the interface was the cause of my problems.)

I had deleted that adapter and no evidence remained of it, but I still suspected something wrong with networking. It may have been because I had followed these instructions and created a fake network adapter to use for connection sharing. The last one was my most helpful clue: something was up with my computer's networking settings. This is likely due to a resource shortage and a reboot may be required.'. Audacity failed to start with 'The Audacity IPC server failed to initialize.Adobe Premiere crashed on startup during 'Initializing Application', before even opening a project.RStudio Desktop failed to start, giving error messages ERROR system error 49 (Can't assign requested address) OCCURRED AT rstudio::core::Error rstudio::core::http::initTcpIpAcceptor(SocketAcceptorService &, const std::string &, const std::string &) src/cpp/session/http/SessionPosixHttpConnectionListener.cpp:103 LOGGED FROM: int main(int, char *const *) src/cpp/session/SessionMain.cpp:2088.I had started encountering crashes on startup in multiple apps that all had networking issues at the core:

Audacity macos big sur