Yes, it's different from "мягкий знак" and probably exists more for historical reasons and is used much less frequently. It's a "hard" one even for native speakers and is used only for writing.
If you leave the hard sign out of "съел" (he has eaten) it becomes a different word "сел" (he has sat)
As it's explained on wikipedia https://en.wikipedia.org/wiki/%D0%AA#Modern_Russian:_Hard_sign
"In modern Russian the letter "ъ" is called the hard sign (твёрдый знак tvjordyj znak). It has no phonetic value of its own, and is purely an orthographic device. Its function is to separate a number of prefixes ending in a consonant from a following morpheme that begins with a iotated vowel. It is therefore commonly seen in front of the letters "я", "е", "ё", and "ю" (ja, je, jo, and ju in Russian). The hard sign marks the fact that the sound [j] continues to be heard in the composition."
I agree with everything you said, and I'll add that before the Bolshevik Revolution, every word that didn't end in a ь (мягкий знак) by default ended in the ъ (твёрдый знак), including written names. The Bolsheviks got rid of those (and shortened the printed War and Peace by something like 36 pages!), but you can still see them in old books, on old buildings, and gravestones. And if it helps, the ъ is typed with the ] (square closed parenthesis) and ё is typed with the (backslash) on my keyboard, which I believe is the standard Russian keyboard (definitely not the phonetic one).
You could use the On-Screen Keyboard in Windows, which allows you to do a visual selection of character you want to type:
I got to meet him once when he came to the ICon (an Israeli sci-fi & fantasy convention) years ago. It was pretty interesting, even though I’d never read anything he’d written, nor have I to read any now. In part it’s because I hate reading translation, I always feel like something is missing... but that’s what the Polish Duolingo course is for ;Þ
Suffice to say, it could just as well be a "valiant Soviet fighter" or any equally flowery rephrasing. You cannot eat a meataphor, though. Воин generally means soldier in about the same situations when soldier, man, fighter, warrior, and combatant all mean roughly the same.