How to disable copilot on microsoft office (excel, word, ppt) on Macbook

You can't.
End of story.
You gave permission to Microsoft to install spyware on your computer and there is no 'off' switch or way to remove it except by downgrading the app.
Users on Windows do apparently have an 'off' option but Microsoft have not yet explained whether this entirely turns off Copilot or if it just turns off the helper interface. In other words, if when turned off, it is still stealing your work in the background.

It's definitely a conundrum. I'm less and less comfortable with having my work and personal files open to MS products. They're ubiquitous in my area of work so I have felt obliged to use them, but... I'm starting to explore other options. I've used Pages successfully on Word files and can save a Pages document in Word format without a problem. I've yet to look into some of the open-source equivalents of Word, but this might be what gives me the incentive to do that.

A fair number of lawyers and other individuals whose professions demand confidentiality in their workplace have brought it to Microsoft's attention that this unannounced rollout represents a horrendous monkeywrench in their capacity to maintain it. Like, to the point that using any Office 365 product leaves them exposed to serious professional liability. If insurance companies start canceling liability insurance because of this exposure, whoever authorized this very poorly planned rollout is going to lose their job. (and... it suddenly occurred to me just writing this that I'd be included in that! My liability insurance likely wouldn't cover me if my clients' unpublished written works were captured, even if just for AI training! Makes me doubly glad to have moved back to "classic" Office and it definitely suggests I need to start researching Office alternatives.)

You know, if I went into a healthcare clinic that had an open office plan such that every person getting an exam was right in front of me, I'd turn around and leave. This is like Microsoft waving a magic wand and removing all the walls in a healthcare clinic while people were using it, and I absolutely don't blame anyone for being enraged. I don't know whose idea this rollout was but they sure enough didn't think it through. Something I've unfortunately been seeing more and more of recently—they get smart people who know web architecture to code up something cool and they don't stop to think about how it's going to be perceived and used in real world situations.

https://www.youtube.com/watch?v=W9X6yMwmMpE

Is also very interesting

TOTALLY agree. The way this invasive launch has been handled by Microsoft is CRIMINAL.