Your solution contains UB when called with an empty string as input. Did you test your solution in your IDE with an empty string ""?

Yeah, maybe. We don't know.

Seeing your code would help tho. Or at least knowing the language.

my code keeps outputting runtime error even though when i do it on the ide, it runs instantaneously.?

Please use appropriate markdown formatting and flag your comment as a spoiler when posting code. See https://docs.codewars.com/training/troubleshooting#post-discourse.

it's like every attempt fails lmao, idk why

Reread the description, your solution doesn't meet one of the requirements.

No. Actually by using toLowerCase(), you are doing alright.
You might as well use toUpperCase.

"ignore letter case" means that when you compare two letters for equality, it does not matter what case they are. For example, S and s should be treated as the same.

Because this is the specification. In this problem, words like "Anita" or "Shrimps" are not isograms.
The same or different "unicode characters" is not really relevant. "unicode characters" is a technical thing, while "letter" is more of a language concept. Bringing technical concepts into the domain of the problem is a mistake.

Can we really ignore case in this kata. Upper case character and lowercase characters are different unicode characters. Why does he say ignore the case?

I considered the "case sensitive" part and do it that method for strings in consequence so it considers same letter and still fails for me...

Look at my code, pls

Ignore letter case

not a kata issue. your code fails for e.g. "moOse"

There is nothing to fix (well, I restored a sample test in the description, someone messed it up, but that was a sample test too, so you should have seen it), neither in the description nor the tests, and I already explained what that means, bye.

Ignore letter case means a capital letter is the same as its lowercase version. How you handle that, it's up to you. Not a kata issue.