The application is a challenge to sections of the Northern Ireland Troubles (Legacy and Reconciliation) Act 2023, which received Royal Assent on 18 September 2023. See also the Explanatory Notes issued by the UK government.
The European Convention on Human Rights enables Ireland to seek enforcement of human rights no matter who holds power at either Westminster or Belfast. Human rights underpin much of the 1998 Belfast (“Good Friday”) Agreement.
This is one to keep an eye on although it is perhaps unlikely that much will happen before the next UK general election.
The European Court of Human Rights Press Release provides fuller details .....