Where can I find the Ministerial Decree published on 18 September 2020 that you are referring to?

You can find the Ministerial Decree of 14 September 2020, published on 18 September 2020, on the government website (in Dutch).
On 21 December 2020, the Ministerial Decree was extended until 1 July 2021. You can find the update of the Ministerial Decree on the government's website (in Dutch).

On 29 december 2021 a new Ministerial Decree was published.