There is very little evidence of a correlation, less of a causative relationship.

Federal states include some very rich countries: USA, Germany. Some countries with middle levels of income: Argentina, Malaysia. And some extremely poor countries: Sudan, Ethiopia.

There are rich countries with a unitary government (France, Japan) and poor ones (Mali, Laos)

Federal governments don't appear to be significantly different in income than Unitary governments. The ability to move to a state where the laws are different does not seem to greatly affect gdp.

There is very little evidence of a correlation, less of a causative relationship.

Federal states include some very rich countries: USA, Germany. Some countries with middle levels of income: Argentina, Malaysia. And some extremely poor countries: Sudan, Ethiopia.

There are rich countries with a unitary government (France, Japan) and poor ones (Mali, Laos)

One can argue that there are confounding factors (such as war) that could be hiding an underlying trend

Taking countries within one region, one can compare Chile and Argentina. Chile is a Unitary, Argentina is Federal. These are two neighbouring countries, with related histories, culture and language and climate. One, Argentina, is Federal; the other, Chile, is Unitary. If federalism caused economic growth we would expect Argentina to be significantly richer than Chile. In fact, the GDP/capita of the two countries is similar, with Chile currently slightly wealthier than Argentina. This gives no evidence that a federal country makes greater economic growth.

Federal governments don't appear to be significantly different in income than Unitary governments. The ability to move to a state where the laws are different does not seem to greatly affect GDP.