You don't need software to file taxes. You can download the forms (1040, etc.) from the IRS website (and your state IRS's website), fill them in, print them out, and mail them to the IRS. It costs a few (literally a few) dollars for the postage and a certificate of mailing from the USPS as proof that you had the forms sent out by the deadline.
The forms are not super straightforward but not incredibly complex either. For most normal people with a W-2 or 1099/self-employed income, retirement savings accounts, and some brokerage/investment accounts, you should be able to get it done in a weekend of research & work using resources on the internet, referencing the IRS's instructions for their forms, and using your previous year's return as a reference. And less time in future years once you've figured out how it works. You will need Adobe PDF software, but it's libre and a Windows virtual machine with the network connection disabled will solve that if you use Linux on your computer.
It's not for everyone, but if you don't want to support the evil tax industry in the US (there have been a number of posts on HN about this) then it's a good option.
Additionally, you can create an account on Turbotax and fill in all your information (but with fake name, SSN, employer tax numbers, etc.) and it'll tell you the amount of remaining tax obligation / tax return that it calculates. So you can use that to verify that you did everything properly. Turbotax only charges money to actually submit the return through them; even if you would normally require a paid TurboTax plan (e.g. for contractors, living in multiple states, etc.) you can still go through the process and get the final number without paying.
I did this for the first time this spring and was able to get it done in a weekend. I had W-2 and 1099 income/deductions and lived in multiple states last year. From what I can recall, basically the form 1040 is the 'root of the tree'; your W-2 income goes into that and every other taxable/deductible thing you do ends up aggregated into the 1040. The schedules (A,B,C,...) of the 1040 are like the first level child nodes; each one has a different topic(s) like self employment gains/losses, farming/fishing income, etc. so you can skim over them and see what applies to you, then fill out the ones you need to and enter their totals back into the 1040. The schedules will have lines into which you aggregate specific incomes/deductions, and the instructions for the schedules will have details on how to calculate all of that. And for other special deductions there are lines in the 1040/schedules that mention them. I'm not a CPA so don't blame me if you follow those instructions and something goes wrong.