On 1 January 2021 Northern Ireland will leave the transition period with the rest of the UK and so will remain in the UK VAT Area but it will also remain part of the EU VAT Area for some purposes under the terms of the Northern Ireland Protocol.
This could be extremely complicated for businesses that trade in goods from Northern Ireland or who trade in goods via Northern Ireland to or from the EU.
If you think your business will be affected you should read the guidance at https://www.gov.uk/government/publications/accounting-for-vat-on-goods-moving-between-great-britain-and-northern-ireland-from-1-january-2021?utm_source=b436421e-f800-4b94-a32b-4b036782a7d3&utm_medium=email&utm_campaign=govuk-notifications&utm_content=daily