Two somewhat popular cartoons seem to be ending, The Amazing World of Gumball and OK K.O.
Gumball's ending was noteworthy in that it ended with the literal beginning of the end of the world in which it takes place. Some fans have speculated that the writers are hoping to get approved for a movie to give the series closure, but this seems to be pure wishfulness at this point.
OK K.O. has not actually been canceled or renewed for season 3, but there are two main rumors floating around about why it's unlikely to return.
The first rumor is that OKKO is directly competing with Steven Universe for renewal status, and SU just has the better ratings.
The second rumor is that OKKO hired a known loli artist for their staff, and when challenged on it multiple staff members publicly defended both the artist and his art, thus creating irreconcilable differences with the network.
Either way, OKKO second season ended with several unresolved story arcs and big mysteries unanswered, which has left fans somewhat disgruntled. Though at the same time, a major chunk of season 2 was spent on pure filler episodes, full of nothing but memes, references, and weak jokes. We really can't blame the network for not allowing the show to wrap things up when they squandered so much of their resources.
In other news, Final Space Season 2 is set to begin on the 24th of this month, so I will likely be re-watching the first season soon.