After you file

You do not mention when you filed the 2018 return, but if it happened in 2020 then the only way you could have filed a 2018 return would be by mail, since e-filing for a 2018 return closed more than a year ago.

For a mailed return:

The IRS has just started to work through millions of mailed returns that have been piling up in trailers during the pandemic.  All you can do is watch the IRS refund site to see when your 2019 return makes it to the surface and goes into processing. Sorry.

Per the IRS website IRS Operations During COVID-19: Mission-critical functions continue:

IRS operational status and alternatives

Processing Delays for Paper Tax Returns: Taxpayers should file electronically through their tax preparer, tax software provider, or IRS Free File. 

We’re experiencing delays in processing paper tax returns due to limited staffing. If you already filed a paper return, we will process it in the order we received it.

Do not file a second tax return or contact the IRS about the status of your return.

If  you mail a tax return (or a payment) to the IRS, it is a good idea to use a mailing service that will track it like UPS or certified mail so you will know it was received.

The IRS refund site does not show information for 2018 returns--only 2019, so you are not going to see anything about a mailed in 2018 return.  All you can do is wait patiently for the return to make it to the surface of the pile and be processed.  TurboTax never receives information about your tax returns -- e-filed or mailed-- after you file.