How to turn off imessage delete confirmation on Apple computer?

You can't turn it off.

The messages are on the phone too, so why the extra default box on the computer just to delete a text message?

If you are using iCloud Syncing for Messages, once you delete the message on one device, it's deleted on all of them. That's why Apple added this additional step.

Use Messages in iCloud - Apple Support

You can, however, let Apple (who doesn't read here for suggestions), your thoughts on the matter:

Product Feedback - Apple

Likely there is no feasible hack possible. It is likely the the confirmation is part of the macOS that is signed and sealed Systej Volume and can't be changed by the user. The following is from:

https://eclecticlight.co/2021/12/16/boot-disk-layout-in-macos-monterey/

actionjackson3 wrote:

I don't use iCloud. Is there any way to hack it out through Terminal?

It has nothing to do with whether or not you use iCloud. The conformation was a feature that was added when syncing service was released so as to avoid huge numbers of people losing their minds when they deleted a message on their iPhone thinking it would remain on their Mac (or vice versa), as you assumed.

I've already contacted Apple about product feedback, but I don't think they read those either.

They do. However, this feature has now been in place for several years so, it seems unlikely that Apple is getting the tsunami of requests to change it that might lead them to consider doing so.

Apple can't please everyone all the time. And, they do not have history of providing the ability to turn on or off every feature.

actionjackson3 wrote:

Thanks for the reply, but that doesn't help. There was only one question asked & nothing you wrote addressed that.

I believe I answered that in my first post. "You can't turn it off".

Asking on these Apple Support Community which is Hosted By Apple to " Hack " the OS - is that a genuine question