Low chance of an audit doesn't mean NO chance of an audit.   Most IRS changes are due to user input errors or missing income which is not a program error and the "audit meter" cannot possibly know of them.   That is a marketing ploy to get you to buy the Audit protection and not an insurance plan to avoid audits.

If the IRS is correct, you do realize that if you had originally done your taxes correctly, you STILL would have owed close to that amount ($30,000 minus any penalties and interest) when you would have filed the original correct tax return, don't you?

Turbo Tax is a self prepared return.  It has no way of knowing or checking that you entered something wrong or in the wrong place or entered something twice  Or left something out.  It doesn't check against any outside sources.  The IRS has copies of all the W2s and 1099s your employer and banks/brokers, etc. sent in to match against.  Turbo Tax only checks the calculations of what you entered.   It is your responsibility to check it over before you file.  They only Guarantee that the calculations are right based on the entries you made.

I sense/ understand your frustration..IF the IRS correctly assess you  ( otherwise you need to prove to the IRS that you are correct, with documentation) then your filed return needed correction -- perhaps you overlooked something.  TurboTax is a piece of software  that helps you prepare and file your return. It guarantees the mathematical accuracy based on your input.  For sure  sometimes  and in very complicated cases, it can make mistake by not asking the right question and/or not understanding a nuanced reply -- but those are very rare.  Perhaps , and especially if you disagree with the IRS, you need to visit your local tax professional for advice -- $30,000 is a lot of money