Look it up its called informal economy or shadown economy. Its an illusions
Think about if a person can work for cash and hide their income, how many do that in countries around the world. Who accounts for embezzlement and illegal money.
I am not a economists but I know that the so called rich people lists are lies. Musk even mentioned Putin is significantly richer than him. If Stalin was a trillionaire imagine Putin? Hassan Shiekh could be worth billions. I know the leaders in South Africa are billionaires.
They do not report black markets, prostitution, drugs etc. China grossly inflation their economy.
Gdp is an illusion.
Hamas are billionaires. First world is a illusion outside of health and warzones.