Find the file "config.php" in the nuke root folder.
Locate this line

Code:

$advanced_editor = 0 ;

Change it to

Code:

$advanced_editor = 1 ;

No site told me to do this, I found it through trial and error. FYI, I didn't downgrade to 7.6 or anything, just kept it at 7.7. It seems to work fine when I did it this way. It should be the same for 7.8. Check and tell me if it is