Ukraine has been with primarily American support.

Did you check this link?

https://protectukrainenow.org/en/report

The problem with your statement: it’s too simple and thus simply false. The sum of support from other allies considerably exceeds US support. The US is the biggest among donors however, and that is a great amount of support.

People often tend to oversimplify the picture. People also tend to memorize the state of affairs at some moment, and assume too long that the same snapshot still applies. The US fell behind when Biden’s bill spent months being stuck in Congress (and lots of it is spent domestically anyway - to replace the supplies being sent to Ukraine - sometimes with newer articles, e.g. ATACMS with PrSM). The US also seems to have something at hand which prevents sending any fixed-wing combat aircraft (my guess: state secrets). After some trying, the sides seem to have agreed that US tanks aren’t appropriate for Ukraine, so they sent only a handful and stopped. However, again after some trying, US infantry fighting vehicles are highly sought after, and they’ve been sending a lot. For some reason, the US is unable to send appreciable amounts of self-propelled artillery guns. But it more than made up by sending towed guns and ammo for guns.

Meanwhile, some European countries which were surprised and unprepared at first (e.g. Germany) have become high-ranking donors in the table, because they got their industry started eventually. Going by percentages of GDP however, one can observe that the biggest contributions relative to their own weight are from countries closer to Russia - other invasion candidates are contributing very seriously.