What is the relevance of communism in geopolitics/geopolitical issues?
I would argue that communism is now relevant only because of the leftover influence of the Cold War. The only relevant countries that are truly communist today are North Korea and Cuba. They are only relevant on a limited level.
Much more important, on a geopolitical level, is the "rise of China" and the tensions between it and the United States. The tensions between the US and Russia are also relevant. Both parties of this tension, for example, make it very difficult for the UN to impose serious sanctions on Iran for its nuclear program.
But these tensions are not caused by communism in the present day. Russia is no longer communist and China is commnist in name only. The tensions between them and the US are, in part, left over from the Cold War when their ideology really was relevant.