What specifically are you having trouble understanding here. The war is between US and Russia, and plenty of US officials have active openly acknowledged it.
RAND published a whole study where it advocated for a proxy war in Ukraine as a way to weaken Russia. We also now know that US also sabotaged negotiations last March that could’ve ended the war. Given all that’s now known, it takes stunning amount of intellectual dishonesty to pretend this isn’t a proxy war.