Every country sets its own laws and conditions for the related residency programs. In principle, there is no effect on your Greek application, if this fulfills the set requirements by the law. In any case it could be useful to ask about the reasons of denial for your own files.
If I was not approved for another country’s Golden Visa, does that affect my application with Greece’s?
Last year I applied for a Portuguese Golden Visa and was denied. I think it might have been due to an administrative error on my end or the government’s. In any case, does that, and how does, it affect my application with Greece?
No, it has no effect.
Please keep in mind that each country has its own perquisites for Golden Visa procedures, so each application does not affect the other.
No effect at all! Each country is different.