In other words, be useful. You don't have to worry about "being good" or "doing good" though many do and it's quite admirable to do so. But that's not the bar you have to clear.
The bar you should try to clear is to be useful. If what you're doing all day is helping people have shelter, or raise families, or be more healthy, or have more knowledge, or even be entertained or amused, you're being useful to people.
If what you do all day ultimately serves to make people poorer, more divided, more addicted, and more unwell, then what you're doing is not useful, it's harmful.
If what you're doing all day primarily contributes, even indirectly, to making people's lives worse, then nothing you do after that will erase it. Arguments to the contrary are just rationalization.
By your definition, selling arms to dictators and using the money to buy a yacht and private security qualifies as "service to humanity."
You emphasize "sustainably", but how is it more sustainable to give 500k/year to capitalism until you don't make that much / retire / die? In either option, that 500k/year is there until it isn't. With charity, you'd help more people but it would be no more or less sustainable.
EA charities estimate that the cost of malaria prevention that will save a person's life for 1 year is ~$150. So what is a 'better service for humanity'? Buying yourself one night of sushi & wine or donating one year of life to somebody who wouldn't have it otherwise?
