BREXIT is a fact
The agreement has a transition period until including December 31, 2020. During this period, you keep your existing rights. You do not need a residence document to continue living in the Netherlands, just a valid passport. Did you receive a temporary residence permit from the IND in March or October 2019? Since there is a deal, you do not need this temporary residence permit. You do not need to keep it or to send it back to the IND. Are you a UK national travelling to the Netherlands to live here after 31 January 2020 (Brexit) but before 1 January 2021? Then the provisions of the Withdrawal Agreement apply to you. Make sure that you can also live here after 31 December 2020.
Invitation from the IND
Because your right of residence has changed as a result of Brexit, you have to arrange your residence after Brexit. That is why the IND will send an invitation letter to around 45,000 UK nationals and their family members who are correctly registered in the Personal Records Database at their town hall. The IND will send out the invitations spread across the entire transition period, and afterwards up until 1 July 2021. It is therefore important that your personal details in the BRP are correct.
In this letter, the IND will invite you to submit an application for residence after 31 December 2020. If your application is approved you will receive a (new) residence document. You will need it to continue to live, work and study in the Netherlands after Brexit. You can use it to show that you can live in the Netherlands.
See also link: Make sure that you can also live here after 31 December 2020