To help clear up some confusion, here's a summary of Superman's audio mixes, and their presence on home video.
As was common with big movies at the time, Superman was released in three main formats: 70mm six-track stereo (4.1), 35mm stereo (2.0 which unfolds into 4.0), and mono (for theatres not equipped with stereo).
However, there's a variant of the 70mm track: a split-surround version (5.1). Based on the article Dr. T posted a couple pages ago, this is the original mix of the movie that was made, and the one that was intended to be shown in theatres. However, both due to a quick deadline and a lack of proper equipment for most theatres to play it back, it was only heard in one or two theatres. (But I'm not really sure what the hang-up here was. Either way, it was 100% a theatrical mix. Whether or not you want to refer to it as the "original" theatrical audio mix is up to you, but it was released at the same time as the other mixes, and was made by the same people. Frankly, it's such a minor thing that I'm not sure why this is such a huge argument in the first place.)
As for the remix, when Richard Donner and Michael Thau were preparing to make the Special Edition, they played Donner's personal print of the movie, and were surprised at how much the mix sounded like mono, so they decided to redo the sound. It's pretty obvious it was the 35mm mix they were listening to, which is known for sounding very poor (Geoff has a good explanation here). If they had heard/used the 70mm mix, then we might not have gotten that remix in the first place, but ah well. The remix ended up replacing/altering a lot of the sound effects.
As for home video formats...
The Laserdiscs all used the 35mm mix, except for the widescreen Laserdisc which seems to have used a downmixed 70mm mix (being notable from its better quality). The 2.0 on the DVDs/Blu-rays/4K are also the 35mm mix.*
Neither the mono track nor the 70mm mono-surround mix have been released on home video. The 5.1 on the Anthology Blu-ray was actually a cut-down version of the Special Edition remix, and the Atmos is mostly an upmix of this. However, the previous 2018 4K did include the 70mm split surround mix. For some reason, WB decided to not include that on the new disc. Why? Who knows. It was discussed here before, and the guess is that whoever was in charge of including whatever audio on the disc didn't know what it was and thought it was redundant. Probably the same reason 2 & 3 also drop their 5.1 mixes, (which are likely the original 70mm mixes, though not confirmed,) and swap them out for their 35mm mixes.