How do I Remove a Person from Sharing on a Mac Studio using Safari?

Block phone numbers, contacts, and emails on your iPhone, iPad, or iPod touch

Yes this pertain blocking on iPhone etc.

Block or unblock senders in Mail on Mac

The method I have used and works just great.

In the Mail Application >> Preferences >> Junk and refer to below image.

Have blocked e-mail address and phone numbers listed and redacted. Some e-mail address are done from Apple Computer and phone numbers from iPhone.

The entire list from Computer and iPhone for Blocking e-mail address and or Phone number Sync accross all 3 Computers and one iPhone

Block messages from a specific person or number on iPhone

1. In a Messages conversation, tap the name or number at the top of the conversation, then tap 
2. at the top right.
3. Tap the name or phone number to view the contact card.
4. Scroll down, then tap Block this Caller.

You are welcome and thank you too.

Do come back to the Apple Support Communities ( ASC )  in the future, if / or when additional questions may arise

Ps - am little slow some times this end and sorry for that

Ok and have attempted to duplication your actions as I understand them.

First image below is any image on the Web and Right Click brings up the circled Options

Second image is specifically from the " Share " option in first image and therein are additional options.

Can you direct me, just what was used, in your instance, to Share and now what to UnShare ?

Thank you and refer to image below with added Text Box.

So the image was Shared via Messages Application - right ?

Perhaps - the actual Share is only sharing in the way that the Image was sent to the recipient and nothing more that exactly that.

AFAIK - there is nothing more involved.

If you what to Block the user/ recipient for further Messages - that is a much different matter

If that is not it - am very sorry but I am just not getting it.

Checklist: If you want to stop sharing with someone whom you previously shared with

Hope I have not miscommunicated in early post - was referring to myself as being a little slow at my advance years 😀