Sophomores and upper classmen can choose off campus living in an apartment or a house.

参考译文：二年级学生和高年级学生可以选择住在校园外的公寓里或者房子里。

参考译文：二年级学生和高年级学生可以选择校外租公寓和房子来居住/住宿。

请问这里的 choose off 是固定搭配吗？

解答如下：

你的理解有误，off不是和choose 构成搭配，而是和campus构成搭配“off campus 在校园外（的）”

I want to move off campus.  

我要搬出去,在校外住.

You should compare prices at the on campus and off campus bookstore.  

你应该比较校内书店和校外书店的价钱.

Students who have cars often drive to restaurants to lunch off campus.  

有车的同学经常开车到学校外的餐厅吃饭.

The critical difference between the two modes of study is off campus.  

这两种学习模式的关键性区别是在校外.

Are the restaurants off campus expensive?  

校外的餐厅会不会很贵?

 I'm going to live off campus if I can find somewhere cheap enough.  

要是能找到足够便宜的地方，我就不在校园里住了。

Students can choose to live on or off campus.
学生也可以选择住在校外。

Why Living Off Campus Is Popular?

校外租房何以流行?

Are the restaurants off campus expensive?
校外的餐厅会不会很贵?

Barry: Kev, let's go off campus for lunch.
柯文,我们去学校外吃午饭吧。

Off campus, they faced hostility.Brig.
在校园之外，他们遭人敌意。

But the disadvantage is that renting off campus is more expensive.
但是坏处是，在校外租房子要贵许多。