It's honestly crazy how people have so many misconceptions about the behind the scenes drama with Invader Zim that's mostly just fabricated based on what we expect because of what we hear happens with other shows.
Like, the network censors did have some weird bones to pick with certain things the Zim crew wanted to do, but I think it should be obvious given the stuff that made it to air that they were actually quite lenient about what was allowed. I think somewhere there's even a quote from Jhonen saying he didn't actually have a lot of fights with them and that the only thing that would've changed if Zim were on something like Adult Swim where he could go totally hogwild is that people would just randomly explode sometimes. Like, Nick were the ones who asked Jhonen to make a show for them after reading his extremely violent and mature comic books. They knew what they were getting into and they knew what they were signing off on when they let episodes like Dark Harvest go to air.
Contrary to popular belief, Nick never "hated" Zim. It wasn't cancelled for being "dark" or getting complaints from Karens or inspiring serial killers or having low ratings, and they certainly didn't try to sabotage it on purpose with their wack-ass scheduling (how would that have benefited them?). Dark Harvest was in like, the third episode and they were mid-production on season 2 when the show was cancelled. It was Nick's most expensive show at the time and while it was getting good ratings it wasn't as profitable as they wanted it to be. So when Viacom's stock tanked and they needed to cut expenses they gave Jhonen a few different options to reduce the budget, and when they couldn't come to an agreement the show was cancelled. When deciding what episodes to finish Jhonen suggested changing the ending of 10 Minutes to Doom to have Zim die in order to give the show finality, but Nick wanted to leave the door open for the show to come back. Ultimately, it was decided that the Xmas episode should be the finale because it would make the most money.
Nick actually loved the show. They got exactly what they asked for and it did well despite the issues they had with scheduling it and their own ineptitude at marketing and merchandising it. When they ran a Zim marathon on Nicktoons Network in the late 2000s the ratings were something like the highest ever or second only to Avatar, and they did reopen negotiations with Jhonen to revive the show again. But they still couldn't agree on a budget so nothing came to fruition. Eventually though, we finally got the comics and ETF and I believe Jhonen said that there was supposed to be a revival series or some other continuation following ETF, but negotiations on that fell through because just when they were about to come to an agreement there was a change in leadership at Nick that caused negotiations to be scrapped.
It wasn't Jhonen and the network who had "creative differences". From what I understand, the only drama with "creative differences" on the show were with director Steve Ressel (and this was waaaaay before he got outed as a groomer in 2020). Apparently, there was enough bad blood between him and Jhonen and the rest of the crew that he said he wouldn't return to Zim if it ever got revived (and in fact he did not for ETF). I think it's actually quite telling that Steve recorded commentary tracks for the show by himself that didn't even make it onto the DVDs while Jhonen and all the writers and actors who were on the commentary tracks that actually got officially released sounded like they all got along really well and enjoyed working together. I think there was also even a conscious effort to avoid talking about Steve in the official commentaries.
Also, there's a whole blog post by Rikki Simons titled "Character Assassination Long Since Past Due" where he reams Steve Ressel for not only being a dick at work but for talking shit on his own platform and being the source of a lot of the misconceptions about Jhonen's attitude toward the show that persist to this day.
