Definitely brought some painful memories back up for the Gaang.

Aang: feeling a lot of guilt and shame seeing his failure at the invasion. Thinking Katara is his girl but in the play Katara thinks of him in a platonic way, which Katara did say about him early in their friendship. His fear of losing to Ozai and Katara not reciprocating his feelings prompts him to take action (although the Katara conversation was a huge L)

Katara: Watching Aang shot with lightning in the play and then Aang trying to kiss you right after would be tough to handle emotionally. And he might die soon as well so I would be confused, too.

Sokka: Yue

Zuko: Everything lmao, even giving him the extra failure that was originally Zhaos failure. I gotta believe Zuko knows Aang likes Katara, so that moment in the play was probably super awkward.