Assuming you invest your money in a diversified index fund like the msci world or the s&p 500 your money roughly doubles every 10 years (on average in the long term). Investing a large sum of money and putting the profits to work can go a looong way and personally i have a feeling that Ukraine will still be feeling the effects of the war 10 years down the line (rebuilding stuff, clearing mines, ect.). This fund could not only help with rebuilding Ukraine, it could also generate funds that can be invested into the countries economy in the long term.

This way they would still on average recieve funds of around $23 billion each year and that for all eternity.

Obviously this is just some quick maths and oversimplifying the situation but generally speaking, if it's for a country or a private person, investing money and putting the profits to work instead of just spending the money itself is not such a bad idea after all.