If you received a delinquent return letter, you are already moving up the IRS food chain. If you don't get something in soon, the IRS will prepare what's called a substitute return and assess you the tax they have calculated. A substitute return is prepared based on the information that has been reported to the IRS. Informational return info form W-2s, 1099-MISC, 1099-INT, DIV, B, etc. You mentioned you have a side business so in the substitute return prepared by the IRS, no expenses would be used to offset your business income. Your tax billing will be crazy high and not correct. That being said, the IRS is in the same boat as everyone else when it comes to Covid. Many agents working from home and no real phone support. This might slow down the collection process for your 2019 return.
You will need to prepare your 2019 return using the desktop software if you decide to use TurboTax and mail the returns in. The online product is only for the current tax year. Here is a link from Amazon for the 2019 Software. There are other considerations to get your return in soon like the 3rd stimulus payment coming up. You will want to something into the IRS to qualify for this payment.
