I’ve got an alternative plan of attack.  Tonight I am going to take the web server down, bring it up under an old backed up images but disable mysql so old database will not be served or altered and new data lost.  Copy the mysql files for nextcloud out, then shut it down, bright up the new, and copy the mysql files for nextcloud in.  It is unfortunately slightly more interrupting than using the command to copy the files out of the old image would have been but I can not remember or find it.