Here’s a good thread on the various audio mixes:
https://originaltrilogy.com/topic/Star-Wars-sound-mixes/id/15294
The mono mix was the last one prepared and has quite a few different sound effects, new lines of dialogue (the tractor beam line extension and “close the blast doors” which were put back in in 1997), alternate dialogue takes (all of Beru’s dialogue), etc. I like it for the differences (“Blast it, Biggs” sounds weird to me now), but the quality isn’t as good, obviously. It was restored from a videotaped recording (or two?) of a TV broadcast that used the mix; it’s never been officially released on home video.
Here’s hairy_hen’s thread about his 5.1 recreation of the 70mm Dolby Six-Track mix (which is the 5.1 mix included on 4K77 and Despecialized):