On Tue, 4 Jun 2019, Ronald F. Guilmette wrote:
Grrr. I can't imagine why this would be so hard. I didn't think what I wanted to do would be so complex. Again, I just want a digital xclock to appear in the blank space below the xbiff thingy in the default theme.
AFAIK there is no such thing as a "default theme" (valid for any fvwm installation anywhere). There could be a "system default" bundled in your OS distro (different for each distro).
You have to locate that, copy it to your ~/.fvwm/.fvwm2rc (so that all the system stuff is now "yours") and try to play with that adding (patiently) one thing at a time.