According to the Statista site, of the approximate 5.8m Nato troops, 1.35m of those are US troops, this leaves the remainder of approximately 4.45m Nato troops based in Europe (including the 0.5m in Turkey), meaning US troops are not quite the majority of Nato troops and the majority of Nato troops are thus based in Europe.
The application of forces is however not so simple as just adding/subtracting overall numbers as in any conflict as not all forces from all sides would be deployed, this is true for both sides. However, the stats clearly show that Nato is far from depleted and far outnumbers Russia in all measures of forces except nuclear.
Unlike the Nato article 5 clause that requires Nato allies to come to mutual defence, there is no such alliance with China, Iran and Russian and I would not be so confident that China nor Iran would send their forces to assist Russia in a direct confrontation with Nato.
