Because of the default permissions, owner, and group of the /opt/xojo folder, it’s not possible for a normal user to save a top-level IDE Script (one that is available in the File → IDE Scripts menu).
To fix this:
cd /opt/xojo
chown root:sudoers xojo202r2.1
chmod 775 Scripts
This will allow your user to save into that folder.
NOTE: The better group would be staff, but neither CentOS, Debian, nor Mint add your default user to the staff group. If you go that route, you will need to add your user to the “staff” group, logout and log back in.