The fed had to create that $100Bn to loan it to the US govt. The US government has to pay going interest rates for debt.
It's a very very expensive choice for something that is not our war.
It's something like $1200 per tax payer[1]. I do not support us funding Ukraine's war to the tune of $1200, personally.
[1] - https://taxfoundation.org/publications/latest-federal-income... ~50% of people even work, and 99% of the taxes paid are by the top 50% of earners. ~350M ppl in US --> $100Bn / (350M ppl * 50% work * 50% pay) ~= $1200