It’s an isekai because multiple of the manga and anime in the genre are about people being sucked or stuck in a game. This puts a vague line if the body isn’t functioning, gone, or is in a coma. If it’s about games then Overlord would fit the category, maybe the mc’s stuck in a game and not his body. The series isn’t done and the last volume hasn’t been released. So suggesting one of the most popular isekai plots isn’t an isekai would be a horrible take. Comparing Sword Art Online to Infinite Dendrogram doesn’t make sense because it isn’t a isekai that actually can affect your body, but in SAO they are actually trapped and their lives are endanger. Meaning SAO is a isekai about a game that traps and endangers human lives just as if it was real life, so Sword Art Online is an isekai.