As of 1 September 2022, as a non-resident taxpayer FOR INCOME TAX PURPOSES it will no longer be possible to request a username and password from the Tax Authorities.
From now on, foreign taxpayers must submit their tax return using DigiD or a national login method via the site of the Tax Authorities. If foreign taxpayers already have a username and password, they can continue to use it until 1 July 2023.
Source Taxence
Note from the editors: For VAT purposes, non-established businesses can still apply for login details for the ‘old portal’ of the Dutch tax authorities. You can find more information HERE