The order form has UK as country of residence when buying a global pass:

But whatever it is, GB or UK, Scotland, England and Wales are all included.

The Republic of Ireland is certainly not included. Northern Ireland might be included but IIRC a journey in NI doesn't trigger an inbound/outbound journey in the app… you can test that after activation if you want (be sure to choose a future date, so you can cancel your travel day and the linked inbound/outbound journey if it does trigger one).

You are likely much too young to even know about that: but it is still based on what once used to be state-owned British Rail, before some GB govmt started it to privatise etc. Same-same for all other countries: once they all had simply 1 big state-owned train company (sometimes not even a company as such-a state/ministry institution-just as the mail or the telefones=pre mobile once were).

In Ulster BR never came-it always had its own train running set-up, also for its buses.