I would like to be Superuser on my BeagleBone Green W and Debian 9.9 LXQT - currently I get the message “sudo: /usr/bin/sudo must be owned by uid 0 and have the setuid bit set” when I try.

How could I change these permissions and become superuser???

This answer seems appropriate:

Login as root and if you have not changed it use temppwd as the password then

chown root:root /usr/bin/sudo && chmod 4755 /usr/bin/sudo

exit and login as debian

In the future if you want to become superuser for a time use

sudo -s

When done as superuser enter exit to return to debian