Partially correct, as I understand it. Hyphens (the shortest of the three types of dash) join words or parts of words. EM dashes (the longest of the three types of dash) are used to subdivide a sentence into clauses. The EM dash can be used in lieu of commas, or in lieu of parentheses for this purpose.

The EN dash is neither a hyphen nor an EM dash, and should not be used where a hyphen or an EM dash is called for. The EN dash is used for things like punctuating ranges of numbers (as in "1937–1942") or separating the numbers in sports scores ("The Bears beat the Bengals by a score of 36–28"). In some instances, the EN dash is also appropriate for separating a prefix to a proper noun (as in "pre–Renaissance").

I'm basically familiar with the Chicago Manual Of Style, and the CMOS does NOT call for spaces between words and any kinds of dashes.

https://www.chicagomanualofstyle.org/qanda/data/faq/topics/HyphensEnDashesEmDashes/faq0002.html

IMHO, the fourth version is correct, the first three are not. I don't view it as a question of preference, I view it as a question of which is correct and which are not correct.

I'd second this but would add a rider that correctness is contextual - e.g. as to dialect and form - the Chicago Manual of Style doesn't apply to a hairdresser writing an email in the Cape Town Flats. Or to an Englishman typing into a web-form.

I'd suggest the Em Dash is already dying due to it being in the ASCII symbols but not on the QWERTY keyboard - something it has in common with curled apostrophes and speechmarks.

We'll be left with - ' ". And that's fine - typography mustn't become more than a means to an end, or a way of encoding snobbery around who may and who may not write. Are we really saying we'll throw someone's manuscript back at them because it has 1937-1942 rather than 1937–1942? Wouldn't that be punishing the other person for not having been passed a hidden caste-mark by another member of a literate elite?

The Ctrl + Alt + _ shortcut doesn't seem to work for me (in this text box or on LibreOffice). Would the OP mind checking if it isn't specific to certain word processors?

It didn't work for me, either -- using Word 2019 on a Windoze computer. What does work -- in Word and in SoftMaker TextMaker but not in LibreOffice Writer -- is CTRL+number pad '-' for an EN dash, and CTRL+ALT+number pad '-' for an EM dash.

In LibreOffice Writer, the following is from the LibreOffice manual:

The above also works in Word 2019 (on Windows), except that Word isn't smart enough to use an EN dash between numbers if you don't type the spaces (which is not a correct format for ranges of numbers). It doesn't work in TextMaker 2021.

Manuscripts are manuscripts, not books. I'm old enough to remember when manuscripts were typed on mechanical (and then electric! Woo Hoo!) typewriters, and italics were indicated by underscoring the text. (And underscoring was a multi-step operation -- first you typed the text, then you backspaced to the beginning, then you typed a batch of underscore characters until you reached the end of the selection.) Most word processors automatically replace straight quotation marks (primes) with "curly" quotation marks if the typeface offers them, so that's not an issue. In traditional publishing, a book designer or typesetter takes care of converting double hyphens to EN or EM dashes. In the self-publishing universe, the author usually is the book designer and the typesetter, so it's best (IMHO) to learn the differences among hyphens, EN dashes, and EM dashes, and learn how to create them (if your word processor doesn't do so automatically).

I'm rather anal about using the right type of dash (and in the generally-accepted "correct" format) in my books. I'm more likely to cheat and cut corners when blathering away on Internet forums.

According to TeX style, when writing in plain ASCII in such a way as to maximise ease of conversion:

• Hyphen or a minus is one dash: "-"
• En-dash is two dashes: "--"
• Em-dash is three dashes: "---"

(Of course some style guides in some languages don't use the em-dash much, if at all.)

In Windows, Alt+0150 (on the numeric keypad only) makes an en dash, and Alt+0151 makes an em dash.

It's a PITA on laptops that don't have a numeric keypad—and if there is a number pad, it needs to be configured for numbers and not arrow keys.

I used a program called AutoHotKey to program every computer in the house and office to interpret RightAlt-minus (as inscribed, regardless of any active alternate language layout) to produce en dash and RightAlt-equal an em dash. (The ones next to Backspace.) Unfortunately, although you don't have to be a programmer per se, you do have to have enough of that inclination to figure out how to do that in AHK's pseudo-code. It's amazing that Windows doesn't have an easy built-in mechanism for assigning unused key combinations that way. Does Apple world?

I also made AHK interpret a "click" (downpress) on the mouse's scroll wheel to swap the buttons back and forth, so that when one hand or shoulder starts to tingle, I can switch mouse hands for a few weeks and still use index/middle as primary/secondary click.