I understand your frustration. I also understand the problem as you see it.
The original answers & I fear yours maybe the same, isn't addressing the original problem.
It actually may be, because the problem stems from creating html content in a word processor. The fact that it seemed to work well for you in the past, may just be happy coincidence.
I would create a table, like this one...in Word as it's the easiest way of doing it.
...As for the 'paste from Word' option, that gives exactly the same results as the notepad option, so why would I use it?
Well, that's pretty much my point. I think it was probably esmi's as well. You're still insisting on pasting formatting generated by a word processing program into the editor.
As I've come to realise with WordPress, it's just like Apple & Microsoft. Updates are rarely thought through & are released because they're shiny & look good.
I can tell you from literally hundreds of hours of personal experience working with WordPress, that isn't the case. I think what's actually happened there, is that you've encountered a change that no longer lets you do something that wasn't really intended to be good practice (but was a convenience for you) to begin with. The point is, Microsoft Word is a word processor. Not a tool for creating clean code for web pages.
Are you sure it's actually wordpress that's placing the 'nowrap' code in your your document? Is it possible you've accidentally set your table properties to nowrap while creating them in MS Word? Simply dragging a table while in an MS Word document might be enough to change the wrap properties. It seems to me a more likely scenario that the nowrap is being added during table creation, rather than during publishing. Is that possible? Or am I interpreting what you are seeing relative to 'nowrap' in your source code incorrectly simply because I can't view a sample of your source code?