Actually, the (capital-O) Orthodox churches don't believe in original sin at all.
I was referring to small-o defining orthodox as “conforming to the usual beliefs or established doctrines, as in religion, politics, etc.; approved or conventional [orthodox ideas]”.
Let's consult their Catechism:
Because all have come of Adam since his infection by sin, and all sin themselves. As from an infected source there naturally flows an infected stream, so from a father infected with sin, and consequently mortal, there naturally proceeds a posterity infected like him with sin, and like him mortal.
I see a desire by many Orthodox to try to differentiate themselves from Catholics by any means they can, even if it strains their own teaching.
With regard to original sin, the difference between Orthodox Christianity and the West may be outlined as follows:
In the Orthodox Faith, the term “original sin” refers to the “first” sin of Adam and Eve. As a result of this sin, humanity bears the “consequences” of sin, the chief of which is death. Here the word “original” may be seen as synonymous with “first.” Hence, the “original sin” refers to the “first sin” in much the same way as “original chair” refers to the “first chair.”
In the West, humanity likewise bears the “consequences” of the “original sin” of Adam and Eve. However, the West also understands that humanity is likewise “guilty” of the sin of Adam and Eve. The term “Original Sin” here refers to the condition into which humanity is born, a condition in which guilt as well as consequence is involved.
In the Orthodox Christian understanding, while humanity does bear the consequences of the original, or first, sin, humanity does not bear the personal guilt associated with this sin. Adam and Eve are guilty of their willful action; we bear the consequences, chief of which is death.
One might look at all of this in a completely different light. Imagine, if you will, that one of your close relatives was a mass murderer. He committed many serious crimes for which he was found guilty—and perhaps even admitted his guilt publicly. You, as his or her son or brother or cousin, may very well bear the consequences of his action—people may shy away from you or say, “Watch out for him—he comes from a family of mass murderers.” Your name may be tainted, or you may face some other forms of discrimination as a consequence of your relative’s sin. You, however, are not personally guilty of his or her sin.
https://oca.org/questions/teaching/st.-augustine-original-sin