BEIS have provided an update on use of the UNKI mark here https://www.gov.uk/guidance/using-the-ukni-marking-from-1-january-2021
This also includes a useful table to show the markings acceptable in GB, NI and the EU both during 2021 and from 2022 onwards. Note that where products comply, you can apply both CE and UKCA markings to allow the same product to be traded in all UK and EU markets. Products with UKNI markings have more restrictions, the UKNI marking must be used in combination with CE and those products cannot be placed on the EU market.
