Thumpalumpacus
Major
No. It is NOT a proxy war. It is a war of national survival for Ukraine resulting from Russian aggression. Nothing more, nothing less.
Sapping China was certainly not on the Western mind when we decided to support Ukraine in its defensive war. Chinese arms weren't being supplied at that time., and so I doubt that was any motivation in DC, Brussels, London, etc. I.E. from the Western perspective this is not a proxy war at all.
Now, if China has since actually decided to supply arms to Russia, that could indicate that China sees this as a proxy war even if the West doesn't. And to be fair, if the Chinese are supplying arms to Russia, that could change this into a proxy war even if the West didn't aim for that. After all, Chinese weapons sent to western Russia are not Chinese weapons that can threaten America's Far East allies. That still doesn't mean that America sees it as a proxy war, but reality has a way of imposing its own stamp and it could become that despite Western intentions solely to help Ukraine rather than sap China.
Different supporters can and often do have different reasons for providing lethal aid. America's support of radical Muslims in Afghanistan, for instance, made that a proxy war for us with the purpose of sapping the USSR; but for the USSR, it was still a direct war with the goal of political control, with their own direct involvement.