Beginning in 2021, it will no longer be possible to file requests for withholding tax adjustments on account of additional deductions (e.g. pillar 2 buy-ins, pillar 3a contributions or debt interest). 2020 is the last tax year for which a withholding tax adjustment can be requested. For this reason, you should check with your tax advisor whether it still makes financial sense to pay into a pillar 3a account starting in 2021.