BluesBrother : Whether today [political voting for governments] is a disfellowshipping matter , I am not sure .The Shepherd the Flock book is not specific.
The book Shepherd the Flock of God, 2019, p.153 refers to actions that may indicate disassociation. These include :
(4) Taking a Course that Violates Christian Neutrality: (Isa. 2:4; John 15:17-19; lvs pp. 60-63, 244) If he joins a nonneutral organization, he has disassociated himself. If his employment makes him a clear accomplice in nonneutral activities, he should generally be allowed six months to make an adjustment. If he does not, he has disassociated himself.
That seems to suggest that it is only joining a nonneutral organization which would be viewed as disassociation. However, How to Remain in God's Love (lvs) chapter 5 para.1-4 says:
How can we be “no part of the world”? In this chapter, we will discuss several ways: We remain loyal to God’s Kingdom and are neutral, that is, we do not take sides in politics... Ambassadors represent their government in a foreign land, so they do not get involved in the politics of that land...Clearly, no true Christian would get involved in the politics of this world.
It doesn't actually use the word "vote" or "voting", and so there might be some discretion allowed, but I think the message is clear enough.