except that idiom
B1 （用于说明为什么某事不可能或者不真实）只是…，不过…
used to give a reason why something is not possible or true
I want to go, except that I'm tired. 我想去，只是太累了。
The exam went pretty well, except that I misread the final question. 我考试考得很好，不过我看错了最后一道题。