How does one determine a REAL WORLD cash flow from the tax return. Is there a universal line item or formula to use from the 1120?

Assuming I'm using significant leverage, what is really there to support debt payments? Thus far I've heard from different sources to use M1-1, M1-10, or 1120 "taxable income" as the starting point for addbacks. Would love to get some alternative perspectives from the financiers on the forum.

For context, Im coming from the public markets, so have only ever used financial statements to do analysis. I'm trying to be able to understand how it translates to the tax returns that banks utilize.