self employed as a pet sitter in 2019. Do not have a w2, 1099, or paystub bec I worked solo and mostly cash or venmo payments. Should I/ can I file a tax return for the year 2019?

Yes, you will have to file a tax return for 2019.  The IRS requires that all income you receive has to be reported.  You will report your income and expenses from your pet sitting business on Schedule C Profit or Loss from Business. TurboTax Premier will allow you to prepare and file your tax return with a Schedule C.