[RPG] find more information on the Gloaming Court/Gloaming Fey

D&D Sources

I think Weckar E. is basically correct in that this confusion stems from the fact that, like many elements of D&D, the fey courts are cobbled together from a mishmash of not-terribly-consistent folklore. There seem to be two competing views:

1. The two courts are basically mirror images of each other - the Seelie project an image of light and the Unseelie one of darkness, but under the surface they are pretty similar, with members of both courts being fickle and beauty-obsessed.
2. A view with more overtones of class warfare, where the Seelie are beautiful and exclusionary while the Unseelie are nightmarish and inclusive.

It sounds like more sources tend toward the first view, but I think there's enough material provided for you to choose whichever one you feel is right for your game.

Other Sources

Other depictions of the two courts that I'm familiar with tend more toward the first view. Often fey from both courts are equally dangerous in their own ways - they merely express their unpredictable personalities and the power of nature differently.

The Dresden Files novels, for example, play up the Summer and Winter connections. The Seelie are bright, colorful, and generally pleasant enough on the surface, but they can also be quick to anger and terrible in their power, like a summer's day giving way to a powerful thunderstorm. Alternatively, they might simply get carried away or be otherwise heedless of the consequences of their actions, turning from pleasant warmth to a dangerous heat wave.

The Unseelie are cold and vicious, but aren't entirely without compassion. After all, winter still has its mild days; it is not an unrelenting blizzard. They still experience some form of love, or at least emotional attachment, and while they might see mortals as playthings most of the time, they may develop a certain admiration for mortals who prove themselves capable of keeping up. Even then, mortals must remain on their guard - it's not uncommon for the Unseelie to have a sadomasochistic streak, and their version of kindness might not seem so pleasant to others.

The Cat Lord is not a deity

Until the 5th Edition Volo's Guide to Monsters, none of the many variations of "Cat Lord" in D&D canon rose past rank 0 "quasi-deity," and even that was only a sidebar'd suggestion in the Epic Level Handbook.

In terms of religious veneration of the Cat Lord, the best attestation I could find came from Dragon Magazine Compendium, in which the tibbits are also said to follow the Cat Lord. Here, the Cat Lord is identified merely as "a powerful creature" and it's noted that the tibbits have no organized religion surrounding her, viewing her as more of an older brother figure and spiritual protector. This includes no details about any religious practices.

...but the tabaxi have other gods

The gods of the tabaxi, at least in the Maztica setting, are Tezca, Nula, Azul, and Zaltec.

• Tezca is a chaotic evil solar deity. He desired fresh human hearts as sacrifices. His faith is a brutal one; each day at sunset, his priests congregate to offer the fresh heart of an unfortunate victim to ensure that the sun-god shall show his face again tomorrow. His faith is related to warmth, life, and power over fire.

• Nula is a chaotic neutral goddess of wild beasts, a demipower whose influence is growing slowly across the Maztican continent. She is invoked by hunters and those who fish, leaving gifts of seed and bone in the wilds for her to know she has been called upon. Primarily depicted as a monkey, she has lesser aspects representing many other animals of the wilds.

• Azul is a lawful evil god of water and rain. Often the first deity enshrined and venerated in new territory (to ensure the rains favor this land and will provide for its people), Azul watches over all bodies of water, from the smallest streams to the mighty ocean, and even the very rare (in tabaxi territories) snowfalls. His priesthood keep themselves scrupulously clean with baths and pumice stones. Foul sacrifices are performed to him in the spring to ensure a prosperous wet season.

• Zaltec is a chaotic evil war god, a vicious deity symbolized by skulls, hearts, blood, and jaguars. Tabaxi who have fallen under the sway of a tabaxi lord (a related creature) tend to worship Zaltec. He is venerated by fresh hearts on his altar, blood spilled in battle, fasting, and ritual scarification. His priests wear black robes, wash their hair in the blood of their victims, and spike it outward in garish diplays. What that might look like, who could say.

Beyond that, though, there is nothing official about the Cat Lord's religion

...because, as noted above, it simply doesn't exist. "Cat Lord" is a well-worn trope in D&D, having appeared in some form in short stories (a group of them appear), novels, the 1st Edition Monster Manual II (the original, a male), Planescape (the second, a female), the Epic Level Handbook (a 37th-level shapeshifting rogue, male) and elsewhere on and off. Until Volo's Guide, however, none firmly attributed deity status to a Cat Lord, and no source that I've found suggests any kind of open worship.

That doesn't mean you can't borrow some...

There are other feline deities, of course - you can look into Ferrix, goddess of weretigers; Bast, a vengeful Egyptian tutelary cat goddess, and Sharess, a Faerunian demipower of cats and hedonism. Any of these might provide a reasonable model for a Cat Lord religion, if that's what you're after.

I hope this has helped.