Connecting to an active desktop in Mac OS?

Question

macOS

Good afternoon! I can’t solve such a seemingly simple thing as connecting to an ACTIVE (I emphasize this) desktop using VNC, on client machines everything is allowed in “shared access” and I log in fine, BUT I connect and log in as a user who is allowed access and from which I know the password!! therefore, a person works on a poppy with his account and password, I don’t know them (the password is so accurate) HOW do I connect directly to his desktop ??