In Armory settings (GUI) I was able to point to the bitcoin blocks database on the external drive.
According to your logfile... Armory is still looking in the default directory (/home/bob/.bitcoin/) for the bitcoin blocks:
2020-12-17 20:28:26 (ERROR) -- BDM.py:268 - setSatoshiDir: directory does not exist: /home/bob/.bitcoin
2020-12-17 20:28:26 (WARNING) -- SDM.py:402 - Spawning DB with command: ArmoryDB --db-type="DB_FULL" --cookie --satoshi-port=8333 --datadir="/media/bob/Backup Plus/Armory" --dbdir="/media/bob/Backup Plus/Armory/databases"
2020-12-17 20:28:26 (INFO) -- ArmoryUtils.py:689 - Executing popen: ['ArmoryDB', '--db-type="DB_FULL"', '--cookie', '--satoshi-port=8333', '--datadir="/media/bob/Backup Plus/Armory"', '--dbdir="/media/bob/Backup Plus/Armory/databases"']
2020-12-17 20:28:26 (INFO) -- ArmoryQt.py:1824 - Connecting on port 9001
2020-12-17 20:28:26 (INFO) -- ArmoryQt.py:1923 - Setting netmode: 1
2020-12-17 20:28:26 (ERROR) -- BDM.py:197 - DB error: /home/bob/.bitcoin/blocks is not a valid path
where did you copy that logfile from? Given you're running Armory using --datadir="/media/bob/Backup Plus/Armory", did you copy the logfile from that directory?
