@pav Just this morning, I think I made some progress.  I noticed that, despite the docs indicating #include’ing the vision.h file being all that is needed, my formed executable was not linked with torchvision, even though it was specified on the linker command line.  As this link: About RegisterOperators in C++ · Issue #2134 · pytorch/vision · GitHub 7 discusses, the linker will recognize that a library isn’t needed and not link with it at all.  That’s what user bmanga’s suggested update at the bottom of that post is supposed to overcome.
That clever way of forcing torchvision to be linked in even if it doesn’t detect any use of the library either wasn’t implemented or else its just not working in my case I think.  So I used the big hammer approach by forcing the linker to use the “whole archive” for torchvision.  On the link line right before specification of the libtorchvision library, I added “-Wl,–whole-archive” and then right after specification of libtorchvision I added “-Wl,–no-whole-archive”.
Now, I can load the torchvision FRCNN without error!
When I try to load my own custom net I get some other errors, but I think its unrelated to this.  So, for now, I think forcing the linker to load the entire torchvision library even if it doesn’t think it is needed seems to get past the issue at hand.