Not a native speaker. Please bear with my English.
Process Lasso will auto switch to high performance mode when I launch a game from Steam, which is really nice.
But some app(not game) from Steam will also trigger this automatic behavior.
Can I just exclude some specific program and still keep the auto high performance mode option on?
I'm sorry, but there's not currently a way to exclude processes from the automatic detection. We'll have to consider that. What Steam non-game processes are you seeing trigger Performance Mode? Sometimes the short-lived helper processes briefly trigger Performance Mode, but it's not generally an issue.
For now, the only thing you can do is turn off the Automatic Game Detection and rely on manual Performance Mode rules, but I know that wasn't your question.