According to mailing lists,

https://www.mail-archive.com/[email protected]/msg33577.html

The new --update=none doesn’t even work correctly and is overwriting files so I don’t think it’s a good idea to use that flag either!

Some of the Debian maintainers discussed this on Reddit a few months ago. They are saying it seems to be a bug and should be fixed in future versions. I don’t know how such a verbose warning message could be a bug, but if I understand correctly that’s what they are saying:

Warning on cp when upgrading
byu/AdbekunkusMX indebian

what are they asking for? cp --update=none instead of cp -n is that?

The warning is NOT a bug. The -n or --no-clobber really is deprecated with planned removal from cp in the future. However, their suggested fix with --update=none has been reported as having bugs.

For this reason, and the fact that --update=none is NOT backwards compatible (it is not recognized on Ubuntu 22.04, 20.04, 18.04 etc) SlickStack has taken another route:

## ss_cp_if_not_exists (avoids deprecated -n option) ##
function ss_cp_if_not_exists {
    command mkdir -p "$(dirname "$2")" && command test ! -e "$2" && command cp "$1" "$2"
}

This approach simply avoids the problems altogether 😉

Ref: https://github.com/littlebizzy/slickstack/blob/master/bash/ss-functions.txt

Because if you try to use --update=none on those older Ubuntu versions, well it will fail and you will see this error:

cp: option ‘–update’ doesn’t allow an argument
Try ‘cp –help’ for more information.

https://unix.stackexchange.com/questions/200283/cp-options-no-clobber-vs-update