YUX-IO Uh, not sure why you are getting this error - the
fof/extend package should be installed when installing
fof/prevent-necrobumping. Can you check that the folder
vendor/fof/extend exists? If it does (or even if it doesn't) try reinstalling the extension with composer.
EDIT: Seeing as you are getting a similar error with fof/pwned-passwords, I'm not sure what the issue is.