It is written in the description as " your task is to find the largest possible product between four adjacent numbers in the same direction" (emphasis mine). You think it is not clear enough?

About the sizes of the matrices, you are right. Throwing large matrices at users tends to result in a poor feedback, and there are ways to make it better. Apparently, the author (or translator) could not be bothered. You can rise the poor quality of feedback on failure as an issue, and it will be hopefully handled some day, by someone :)

1st. Did i miss or in description nothing said about multiplier of 4 biggest numbers in a row(horizontal, vertical or diagonal.)
2dn. It is so hard to test arr 66 by 66 numbers.
Now i googling how to fitt it in my code editor screen, to bee grid like. you write code for 4 by 4 and 6 by 6, and then baaam 66*66. Nice

i wonder, how it would look with Conditional (ternary) operator
// condition ? exprIf True : exprIfFalsev

i thought there would be more than 3 arrays as a test check , but no.
good task