spend a larger percentage of their incomes on taxable goods
Better concepts include a refund or "pre-fund" of the tax value of a given standard of living, offsetting the basket of food, fuel, etc.
People with low incomes save less. That's the basis for the regressivity.
Yes. I guess you could wed a negative income tax to a VAT and claim that the combination is less regressive or not regressive but the VAT part is still the VAT part.
the concept from the mid-90s under the "Fair Tax" label did not have a 'non-taxable goods' category. If you bought something, the transaction was taxed. If you paid for a service, the transaction was taxed.
Monthly Universal Basic income voucher pre-pays the cost of basic goods and services, so low income has a net zero tax burden at worst, net tax income possible.
Prompted me to go online (because the answer surprised me), and I see your answer stated verbatim in a Tax Policy Center piece on this question. I hadn't though it through and was curious about the data that lay behind the answer, but the TPC answer made it quite obvious without the data.