With Steven Universe fans, unsurprisingly, due to the heavy emphasis on LGBT science fiction/fantasy characters and themes, and even similar color palettes in their artwork. There are also the similarities between Spinel and Catra, with both suffering from abandonment issues to the point of attempted omniside. Once Horde Prime gets some screen time, there are a lot of comparisons between him and White Diamond as well.
With The Dragon Prince, another show that attracted former Voltron: Legendary Defender fans that were disillusioned with the fandom of that show. This was helped when the twitter account for The Dragon Prince released crossover sketches made by their artists of the characters of both shows interacting, specifically, Catra and Rayla befriending each other, as well as Soren and Sea Hawk arm wrestling.
With Castlevania (2017), given the parallels between the romance of Vlad Dracula Ţepeş and Lisa, and the friendship between Hordak and Entrapta.
With Ducktales 2017, as both shows are reboots of popular shows from The '80s. Heck, even ND Stevenson was a storyboard writer for DT17's Pilot Movie, and wrote one of the episodes of the first season before moving on to She-Ra. In both reboots, Adaptational Diversity is at the forefront.
There's an overlap between fans of this show and fans of the Carmen Sandiego reboot, due to the similarities between them.
It also popularly shares a fandom with Tangled: The Series, which again, is a show about a heroic princess and her friends while also having Les Yay with her (former) best friend. Even more so when it was revealed that not unlike Catra, Cassandra secretly despised being Always Second Best to Rapunzel and shared the same abusive parental figure with her, eventually leading to her betrayal in search of achieving her own destiny, only to find herself conflicted about being evil and her estrangement from her ex-best friend. A lot of fans even note how accurate Cassandra's Villain Song "Crossing The Line" is in describing Catra, from how the titular princess is blessed and gets everything, all the way to the burning of bridges with her best friend. And much like Catra, Cassandra is left with nothing after driving everyone who once cared about her away and is given a very brutal "The Reason You Suck" Speech by a shapeshifting being who manipulated her, and she's too broken to even care what happens that she practically begs the hero to just give up on her. Interestingly, both Catra's and Cassandra's redemption are notorious for being divisive and have received criticism for being rushed and ignore the scope of the severe damage they both caused.
Despite the major Fandom Rivalry between the shows, there are some fans of Voltron: Legendary Defender who actually do like this show, most notably due to the parallels between Haggar and Shadow Weaver in terms of their sympathetic backstories before they went from good to evil along with characteristic parallels between Coran of the reboot and SPOP's Sea Hawk, or Shiro and Scorpia.
With The Owl House as Luz and Amity are noted to have similarities to Adora and Catra, with the latter having feelings of inadequacy, and having a prickly demeanor towards the protagonist, yet can't bring herself to hate her. Plus, there's some degree of Les Yay between them. Interestingly, it's worth noting that ND Stevenson's wife Molly Ostertag is a staff writer for the show. Even more amusing, both shows had the lead couple (Catra and Adora for She-Ra and Amity and Luz for The Owl House) dancing in prom with one of them wearing a tux and their dance together being the Signature Scene involving the Official Couple of the show! Both shows having big LGBT elements definitely helps.
With Kipo and the Age of Wonderbeasts, thanks to having very similar themes and style. It also helps that the series was ending just as Kipo premiered and that Kipo herself shares a VA with Glimmer.
Gets this a bit with Amphibia, as both shows have a female protagonist in a magical land with a toxic ex-best friend serving the Big Bad's right hand who is trying to conquer said land.
To a lesser extent, there's some viewers who see Anne and Sasha's relationship as somewhat similar to Catra and Adora's. With a few people actually starting to ship them.
Of course, Marcy has netted comparisons with Entrapta, as both are quirky science-minded and show signs of having ADHD and Autism.
The fandom has managed to get along well with the fandom of Hazbin Hotel due to similar themes of redemption, gender identity, abuse, among some. Not to mention that some find Double Trouble to be similar to Angel Dust.
