It was a hot topic amongst fans back when Avatar first aired. Most of the cast was hot enough that anybody could've feasibly been paired with anyone, and there'd be fans of it, and for some fans the idea of their ship becoming canon was obsessively pined for. In particular, the people that shipped Zuko and Katara produced a bevy art and fics and fanatical discussions, they somehow formed a collective culture and came to be known as Zutarans. Back in the day in /co/'s Avatar threads "Zutarans" would be used as the typical boogyman for all things wrong with ATLA and why the show was failing much the same way "tumblr" or "sjws" is used in She-Ra threads today. They weren't liked, honestly considering this bullshit was all over 12 years ago yeah none of it actually mattered.
Zutarans reached a peak of popularity in Season 2 and 3 of Avatar, but an another portion of the fandom reasoned that Aang and Katara would be endgame. There were hints about this all through the series, but it was in September of 2007 when "The Headband" aired that the two groups started to clash. In the episode there's a scene where Aang and Katara share a very passionate, sweaty dance, which fans dubbed the "Kataango", and the more trolly fans would screenshot images of it and show it to Zutaran circles on deviantart and elsewhere and mock them for their ship definitely not going to be canon, and this sparked flame wars and back and forths.
I personally thought it was all silly, and while watching shipping threads before actually watching the show, I thought Aang and Toph should have gotten together. I also pronounced Toph as Toe-f in my head for ages.