You say you did not work in 2018. But you did not meniton whether you had any other income from investments, retirement, etc. If you had NO income then you do not need to file a 2018 tax return. Working in 2019 has no relevance to your 2018 tax return.
DO I NEED TO FILE A TAX RETURN?
https://www.irs.gov/help/ita/do-i-need-to-file-a-tax-return
Who has to file?
http://www.irs.gov/uac/Do-I-Need-to-File-a-Tax-Return%3F
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