Thank you wiedehopf for your help and suggestions.
I think this issue began a few weeks ago, after I ran an extra apt-get command (found in a topic - I forget which). My conclusion was a corrupted system. And, maybe too many incorrect shutdown/restart cycles.
I made a decision to clean up! This included downloading and installing a new Buster img on the SD card. This pi runs headless, so I added 2 files to the /boot directory - ssh (empty) and wpa_supplicant.conf (wi-fi config). After booting up and connecting via SSH, I was able to install piaware and dump1090 and follow abcd567’s instructions on how to restore a feeder-id
The pi & piaware/dump1090 have been humming smoothly since then. Hooray!