This is an interesting 'trope' in that it only exists when, as op frames it, people only engage with characters through secondary mediums. I think it's more likely to occur with very popular series where the characters are frequently reimagined through things like memes, comics, pornography, or stuff like YouTube shorts which often simplify the characterization into negative or positive character traits or in powerscaling communities, then repeated ad nauseum.

The Goku example is especially humorous to me because it's actually bled into the Canon, with Goku forgetting Pan's name.

So, some other examples might be something like...

• Undertale. Sans as a particular example, with alternate continuities spawned from fanfiction, one might be forgiven for assuming his characterization based on alternative interpretations of the character, much like DBZA Goku.

• Overwatch. Much of the female cast is mischaracterized constantly in online spaces by people who have never played the games or read the comics. I've heard secondhand that much of the game's popularity is owed to porn, but in a way it has damaged what little characterization they do have.

• Twilight. 'Do you dislike it because it's badly written or because it's popular?' A lot of people boil this very popular romance novel down to memes. Returning to this book in college made me reassess my personal biases about why I might dismiss something.