ubuntu 20.04 notify-updates-outdated not found
Gustavo, I had the same error with motd. I fixed the problem by installing the update-notifier-common package.
It seems that there is an error in /etc/update-motd.d/90-updates in line 7. Have you edited the file?
The filename should be: /usr/share/update-notifier/notify-updates-outdated!!
That is, the last letter is a "d" not an "s".