What is the most preponderant and correct opinion regarding the ruling on buying money with money, with an increment and a delay, and by analogy, gold and cars, given the disagreement among scholars regarding its permissibility?

The correct view is that the ratio legis (underlying reason or effective cause) for riba (usury/interest) in gold and silver is their function as a medium of exchange (ثمنية), not their weight. Applying this difference of opinion to contemporary paper currency is incorrect, for today's paper currency has replaced gold and silver. Therefore, the assertion that riba does not apply to paper currency today is incorrect. The correct view is that paper currency takes the ruling of gold and silver in the application of riba of both types, in the obligation of zakat, and in the validity of its function as a medium of exchange. This is what has been decreed by various Fiqh academies and scholarly institutions.