Pretend the $20 million is guaranteed, and if anything will increase slightly over time.
What problems could be significantly improved for $20 million?
(I am dreaming of winning the $1.55 billion Powerball drawling. Then taking the lumpsum, posting taxes, investing, and spending 4% each and every year. I understand that the actual may be more, or less than the started amount.)
If I came into an unspendable amount of cash, I would make it my full time job to research things to donate to. Charities, or any charitable organizations, medical research, housing the homeless, feeding/infrastructure/sanitation for poor countries, open source projects, etc. But I don't want to donate to just anyone. I don't want to donate to those shitty fake charities that use their donations to line the pockets of their top people. That's why I would spend a considerabe amount of time researching these groups.
The way I see it, after I buy all the things I want, a house, a fancy car, etc. I couldn't possibly spend more than $1M a year on my family. That gives me $19M a year to donate. I don't really care to keep a cent more.
You are probably spot-on. While I am able to do some things, a charity that is already doing things will likely be better at it.