The US Provided military AID to Ukraine under the Ukrainian Security Assistance Initiative from FY16 on. More than a billion dollar prior to FY 22. That aid included Javelins, as well as Anti Drone capabilities, ISR assets, counterbattery radars, and sniper rifles. All systems that were critical to stopping the Russian advance. We increased those aid packages in 2020 and again in late 2021, pulling anti armor systems out of CENTCOM and either directly giving them to Ukraine under USAI, or dumping them into the Foreign Military Sales program, where we "sold" them to Ukraine for zero down and no payments under the Foreign Military Financing program. "Loans" that were later wiped out in aid packages with no money every changing hands. FMF equipment "sold" in FY20 and FY 21 more Anti Armor systems, MANPADS, and Mark VI patrol boats.
After the the Russians crossed the border on 24 Feb 2022, we stepped up the urgency of the aid and pulled from existing war stocks in EUCOM. The first ammo replenishment crossed the border from Poland the second week of March, 2022. I apologize that I don't remember the exact date, but this isn't a Discord server, and I didn't take pictures of any slides. (this is all unclass anyway)
So Ukraine was getting US military aid for years prior to the invasion, aid packages that were tailored to the observed Russian Capabilities from Crimea, Georgia, and Syria. That aid stepped up in quantity and variety in early 2020 as Putin started saber rattling, and again in late 2021 as Russian troops started massing on the Russian and Belarussian borders, nad the restocking of munitions used to stop the initial advance happened in weeks, not months.
As I said the state of Russian logistics did surprise the west, and that contributed to the ease Ukraine had in stopping the advances, but to say "The Ukrainians started the conflict with stocks of Javelins and other anti-tank munitions, but were chewing through the stocks of what they had purchased, not been given, and used them to help grind the Russians to a halt before the western taps fully opened" is just untrue. That's not what happened.