[margalabargala]

You're not correct. A tertiary definition of "only" is "few". "One of the only" for a member of a small set if perfectly correct in English.

https://www.merriam-webster.com/dictionary/only

[fnordlord]

Of all positive integers less than 10, only 4 are even numbers. 8 is one of the only. right?

[margalabargala]

"8 is one of the only" is a little off because it doesn't have an object, it relies on that being implicit from the prior sentence. "Only" here is an adjective, not a noun. The usage is a little awkward.

It would be more correct to say "there are only 4 positive integers less than 10. 8 is one of them."

[ianburrell]

"One of the only" even has its own dictionary page.

https://www.merriam-webster.com/dictionary/one%20of%20the%20...