I filed an extension on my taxes in the spring and am just completing them now. I intended to make solo 401k and HSA contributions as well as convert a traditional 401k to a Roth 401k last year. Is it too late to do these for tax year 2020?
Yes. Those had to be completed by Dec, 31, 2020. An extension is only to file the paperwork.
yes, you are too late for contributing to HSA or SOLO 401(k) for 2020. the latest date was 5/17/2021. however, if you filed a timely extension for your 1040 then you have until 10/15/2021 to contribute to a SOLO 401(k) but not your HSA.
you can only convert a traditional 401(k) (you're an employee) to a ROTH 401(k) if your plan allows it but it can be done at any time. you will owe income taxes on the amount converted.