The MySQL Shell program complained about an unknown option, even when none were provided when I started it.
$ mysqlsh While processing defaults options: mysqlsh: unknown option --default-character-set
In order to fix this, I simply added the wrongly interpreted option to my defaults file
[mysql] reconnect=false character-set-server=utf8 [mysqldump] column-statistics=0
and started the util with the flag for reading a config file like this
mysqlsh --defaults-file=~/.my.cnf firstname.lastname@example.org:3306