ㄹ 것 같다 vs ㄴ 것 같다.
What’s the difference? Don’t they both mean “I think” or “It seems like?” Please provide examples. Thank you in advance.

Question

Answer

-은/는/을 것 같다 is a grammar pattern for supposition

Verb stem+(으)ㄴ : past tense 
e.g.
먹다 -> 먹은
가다 -> 간

Verb stem+는 : present tense
e.g.
먹다 -> 먹는
가다 -> 가는

Verb stem+(으)ㄹ : future tense
e.g.
먹다 -> 먹을
가다 -> 갈

Literally, 것(과) 같다 means "It is same thing that"
그는 사과를 먹은 것 같다 It is same thing that he ate an apple. => It seems that he ate an apple.
그는 사과를 먹는 것 같다 It is same thing that he eats an apple. => It seems that he eats an apple.
그는 사과를 먹을 것 같다 It is same thing that he will eat an apple. => It seems that he will eat an apple.

Adjective stem+(으)ㄴ : past and present tense 
e.g.
예쁘다 -> 예쁜
좋다 -> 좋은

Adjective stem+(으)ㄹ : future tense
e.g.
예쁘다 -> 예쁠
좋다 -> 좋을

e.g.
오늘 날씨가 좋은 것 같다.  It seems that the weather is good today.
내일 날씨가 좋을 것 같다.  It seems that the weather will be good tomorrow.