New Tax Regime vs Old Tax Regime: An important aspect of opting into the new regime was that once opted in, persons having business/professional income could only opt out of the regime once and thereafter, would be prevented from opting back in.
Old Tax Regime vs New Tax regime: The Union government in Budget 2023 made the New Tax Regime a default choice. If a taxpayer does not choose between the old and new tax regimes, then their taxes will be automatically calculated under the new regime.
Income Tax Returns: The Budget 2023 saw FM Nirmala Sitharaman announce multiple changes in the New Tax Regime. Individual taxpayers can make a switch from the Old Tax Regime to the New Tax Regime as many times as they want. But that's not the same for individual taxpayers with business income.