Yes, you will need to enter EU including NI via a TPE when you're travelling from a third country such as GB to facilitate compliance checks. 

NI: TPEs will be located at the following locations: Belfast Port, Larne Port, Belfast International Airport, Belfast City Airport and City of Derry Airport.

ROI:  Travellers’ Points of Entry: Dublin Airport, Rosslare Port, Port of Cork at Ringaskiddy, Shannon Airport and Cork Airport, and Dublin Port.