thanks - decluttering did it. Is there a general undo?
No, to get something like a new install, deleting the config file will do that. However then you will need to re-install your licensed charts again as well.
The other thing that happens sometimes is the opencpn.ini or opencpn.conf file gets corrupted and simply renaming it by adding .old to the end so you can go back to it or use parts of it. Then restart O and a new fresh ini is made. You will need to adjust settings and load plugins.