The IND has announced that they will be no longer sending out invitation letters. Apparently, they have sent letters to all registered UK nationals in the Netherlands. If you have not received the invitation letter by now, we urge you to apply for a residence permit under the Withdrawal Agreement immediately. Do not wait for a letter from IND.
You can do so online (with DigiD).
The residence permit must be arranged for before 31 December of this year.
The IND is also asking the public to reach out to any British citizens in their neighborhood who might be unaware of this, so they can submit their application on time.
For more information see our main Brexit article.