Made an account just to second this issue. This behavior is absolutely awful.
To answer the questions of the people who keep asking, I will explain exactly when and why this is a problem.
I am trying to copy some text from git. Specifically, I have a line of text that says: `Your branch is up to date with 'origin/my_branch_name'.` I need to copy just the bit that says "my_branch_name". So what I do is carefully highlight "my_branch_name", right click to open the contextual menu, and...... BAM, macos has decided that I actually wanted to highlight 'origin/my_branch_name' instead, so it changes what I've highlighted to include that entire thing, instead of the specific bit of text that I carefully highlighted myself. I can find NO WAY to persist ONLY the text which I have carefully highlighted. MacOS always decides "no, actually you wanted something else" and changes what I've highlighted. So I have no way whatsoever to open the contextual menu just on this piece of text alone.
I am not comfortable using the keyboard shortcut for copy in this context. When I am using a terminal, just to be safe, I never use the keyboard shortcut for "copy", because depending on the context and the terminal you're using, this behavior can sometimes be undefined. For example, if you are ssh'd to a different system, or if you are in telnet, the behavior of the keyboard shortcuts can be different. For this reason, when I want to copy text in a terminal, I ALWAYS right click to open the context menu. But MacOS has decided that this is no longer an option.
This happens in many other circumstances too, outside of the terminal, where I will carefully highlight text, right click to open the contextual menu (because I'm still getting used to Mac keyboard shortcuts), and only too late do I notice that MacOS has decided that I meant to highlight extra stuff.