How did the world lose potential growth by having more savings?

Two seemingly incompatible developments have been seen over the past 20 years: The rise in the global savings rate, and therefore, at equilibrium, in the global investment rate; the increase in the fiscal deficit has only partially used the rise in the private savings rate; The decline in potential growth due to the slowdown in productivity gains. How can this contradiction be explained? Possible explanations are as follows: There has been a rise in the global gross savings rate and gross investment rate, while net capital has slowed: there has therefore been a sharp increase in capital consumption and capital obsolescence; A large part of global savings has been channelled to the United States, a country with very high per capita capital and income, which is therefore an inefficient use of savings; If savings are abundant, there is a lot of investment at equilibrium, and inefficient investments are made (which is consistent with the fall in real interest rates), leading to a decline in productivity gains.