The West isn't sending its soldiers onto a battlefield. They're giving equipment —in many cases older equipment— to a country facing invasion and an existential thread to its sovereignty that is asking desperately for aid. The soldiers using those weapons are members of the Ukrainian armed forces.

When the US armed the Mujaheddin in the 1980s to fight the Soviets, that wasn't Americans shooting at Russians.

When the Soviets and Chinese armed the North Vietnamese and Viet Cong in the 1960s and 1970s, that wasn't Russians and Chinese soldiers shooting at Americans and South Vietnamese.

When the Soviets armed the North Koreas, that wasn't (officially) Russians shooting at the UN forces, even though it was an open secret some of the MiGs were being flown by Russian pilots.

When the Americans did Lendlease and Destroyers-for-Bases in 1939 and 1940, that wasn't the United States entering a shooting war with Germany.

Now things may continue to escalate, and maybe the West does end up becoming active participants in the Ukraine War, but if the Russians think that line has been crossed, they haven't seen anything yet. A NATO attack with modern equipment and modern training used by fresh troops is not what the Russians are dealing with at the moment, and based on the first year of the war, I doubt very much they could deal with it.