since you did not file previous returns, you can expect a notice from the IRS if a capital loss carryover starts showing up on the 2020 return. you need to complete the 2018 and 2019 returns. you'll need desktop software or you could get the forms from the IRS to manually prepare them. the issue is not only that the capital losses were not reported but what about dividends and other income that could use up some of those losses. without proper preparation of 18 and 19, you'll have no way of knowing what the correct CLCO to 2020 is (filed in 2021)
https://www.irs.gov/forms-pubs/prior-year
