Meaning "shape" or "appearance", 모양 is used here to express a particular condition or state.

This expression is thus used when attempting to infer or guess the circumstances of a particular situation after directly seeing it or hearing about it.

It is often used together with -(으)ㄴ/는 걸 보니까 which comes earlier in the sentence and expresses the basis for making the inference or guess.

Details

1. Because this expression is used to express the speaker's inference or guess based upon having seen or heard about the situation being discussed, it cannot be used to describe something the speaker did himself/ herself.

새로 생긴 식당에서 먹어 봤는데 음식이 괜찮은 모양이에요. ✕

2. This expression cannot be used when the basis for the inference is not an objective fact, that is, when the speaker is simply describing something he or she only thinks, or subjectively believes, to be the case.

내 생각에 저기 앉아 있는 여자는 공부 잘하는 모양이에요. ✕

Here, because the speaker is expressing a subjective feeling, -(으)ㄴ/는 모양이다 cannot be used. Instead, -(으)ㄹ 것 같다 can be used to express such subjective notions.

Kimchi Reader

Used to infer or guess a situation after observation.

Details

Usage

Often used with ~(으)ㄴ/는 걸 보니까 earlier in the sentence and gives the reason for the inference or guess.
Not used for talking about yourself (you can't infer/guess about yourself).
Not for subjective thoughts (use 는/(으)ㄴ/(으)ㄹ 것 같다 instead).