For an organization that is lacking in IT Infrastructure development but has the financial capability to acquire it, how would you convince leadership that investing in IT is critical for the growth of the organization?

Building a comprehensive approach. IT infrastructure is related to service and support. Does the company also have the money to ensure proper service and support? Just buying (new) computers is not enough.
On the other hand, cyber-threats caused by old hardware and outdated OS is a big risk, the top management should be at least aware.

I think the best way is being capable to show (using the simplest language as possible) the convergence between business growth and digital transformation. In terms of: How can we scale up our sales, our client digital conversion, optimize and improve our supply chain o internal processes to contribute the revenue generation across sales increase and internal operational efficiency.