"The friend's car is similar."
Translation:친구의 자동차가 비슷해요.
비슷합니다 would be in 'formal' form but this lesson deals with polite form with -요
Is it possible to use ~는 as particle here as well? Or does it have a slightly different meaning?
I don't think you can since the verb here is 비슷하다. You most likely can use 비슷합니다 (it's simply a different speech level), but 비습니다 is derived from a different verb root, so the meaning would not be the same.