How do people really live on Exegol besides the emperor?

It isn't 100% clear yet if any natural corporeal beings were living (for long periods of time) on Exegol.

With the help of the Star Wars Visual Dictionary we can surmise that many of the people involved with bringing The Emperor & The Sith back, were loyalists (Ochi), cultists (Sith Eternal), spirits of the Sith, and alchemist practitioners dabbling in a combination of genetic procedures and the dark side occult.

There is a character called Albrekh for instance, whose a Sith "Alchemist" that fixes Kylo Ren's helmet and The Knights of Ren, who seem to align with The Emperor in the end, are "mildly" force-sensitive. There is another character Rothgar Deng, whose face is distorted from "horrific procedures", and of course there were Snokes in tanks, implying "Snoke Clones".

As for the Sith Troopers, it unclear if they were all corporeal humanoid people and if they lived on Exegol or if they lived on the new Deathstar Destroyers? They were however, placed into legions that were numbered and named after legendary Sith.

The combination of factors may then imply that no one was really "living" on Exogal outside the spirits (wraiths?) and the remains of the Emperor and we might suppose that instead people like scientists, engineers, loyalists, occultists came and went from the planet and/or could temporarily live off of supplies (food, water, shelter, etc) in their vessels.

UPDATE:

In the underground launch bays beneath the surface of Exegol is the final stage of the First Order's long-gestating plan of conquest. the loyalists who have been toiling in secret to bring the return of their glorious Empire and to resurrect the Sith Order include engineers, shipwrights, and enslaved labor. Their efforts have created hundreds of warships and thousands of starfighters ready to launch. While the Sith monolith is the site of macabre rituals that plump the secrets of the Force*, the neighboring staging grounds represent pure military might, grounded in the imperial legacy of rule through technological supremacy."* -Star Wars The Rise of Skywalker Visual Dictionary Page 172

So now that I have my own copy of the Dictionary, I was able to find a passage that specifically tells us a bit more about Exegol.

Exegol had more than one staging ground, meaning that there has to be a separate site near the Sith ruins on the planet where the the children were raised/trained, the scientists and shipwrights came to work, and other slaved labor brought to the planet that we didn't get to see in the film.

But in addition to that the site seems integral for Sidious to be brought back and/or the Force was also on sight and perhaps played a role in other ways, including religious aspiration of the "Sith Eternal" Officers and Personal, who were the must dedicated to the overall cause. (And it appears they were all human).

It doesn't say anywhere if this "neighboring staging ground" is more habitable, than the monolith site, but it does reconfirm my suspicion that there were "ships" and scientists and such that were all working towards this goal and feasibly people could make temporary living structures and/or live on ships.

_{if I come across any more "credible" information, I will update this post with that information.}

This cannot be answered within the context of the film directly, since none of that kind of stuff has been shown on screen.

Not even using the toilet.

This is kind of a trope that real life things are never shown and simply assumed to must have happened/existed, but they arn’t important to the story.

Assuming there were some females on the Death Star one can also conclude that there must have been schools and daycare centers..So Luke literally blew up children...but not many people like to talk about that kind of stuff or that The rebels could be seen as actual religious terrorists...but thats again, besides the point.

Keep in mind on Exegol a fleet of 10,000 destroyers were built underground. It seems obvious there was also hundreds of thousands or millions of beings employed underground and probably planet wide and planet deep.

Also keep in mind we only saw a single (local and tiny) part of the planet (and planets are usually huge) and as soon as Palpatine died the storm also stopped in that area. If you landed in the Sahara via spaceship, it would be a mistake to come to the conclusion the entire earth is a desert.

This kind of movie requires a specific amount of hand waving and suspension of disbelief in order for it to work.