Isn't αυτος this and εκεινος that?
Technically yes but we find that the use of "αυτός" meaning "that" is quite common and accept both "this" and "that".
Why doesn't it accept this? Εκείνος δεν είναι ο σκοπός μου.
It should be accepted now; thanks!
Can I just write δεν είναι ο σκοπός μου, without the subject?
Is this also a valid translation: Ο σκοπός μου δεν είναι αυτός
"Η στόχος μου δεν είναι εκείνος" was offered in a multiple choice - seems like a strange word order, but is it wrong?
Yes, because στόχος is masculine, not feminine -- the feminine definite article η does not fit.