Since February last year, the DUP has boycotted the assembly in protest at the previous Northern Ireland protocol, which Sunak has now replaced to address concerns around sovereignty, disrupted trade and the application of EU law.
Article source: https://www.huffingtonpost.co.uk/entry/why-is-the-dup-hesitant-about-rishi-sunaks-brexit-deal_uk_63ff1a84e4b0ecabbaa257ba