#5 Well, I guess it suits Boris Johnson that there is no real government in Northern Ireland. Without this special arrangement Sinn Fein would now be in government and that would be disastrous for Johnson.
IIRC, Sinn Fein has been in government in Northern Ireland at any time there was a working Executive since the GFA, always as the second biggest party, but that's not really of any concern in practical terms. So, that cannot be it. There hasn't been a "real government" in Northern Ireland for protracted periods, so that cannot be a big thing either...
But now he will use it as leverage against Brussels and want to undermine this supplementary agreement.
Supplementary agreement, as in the Northern Ireland Protocol? Well, that's foreign policy, so the Northern Ireland Executive never had a say in that anyway.
How exactly is it regulated if there is no government in Belfast that is capable of acting?
To my knowledge, if there is no working Executive in Northern Ireland for 6 months, direct rule by Westminster is what is supposed to happen, but this only affects Northern Irish internal affairs, as far as they are devolved in the first place.
Doesn't London then decide the weal and woe of Northern Ireland? Johnson could first tear up the Additional Protocol and then throw it in the wastepaper basket.
Johnson can do that at any time he likes, as foreign policy (and defense, and many others) are Westminster issues, and the Northern Irish Executive, like the Scottish or Welsh Parliaments, have no say in that anyway.
#6 Solange die DUP sich weigert eine Regierung mit zu bilden, ist NI nirgendwo ernsthaft vertreten - kann sich nicht gegen London stellen.
Was auch immer die DUP blockiert, das sind interne politische Vorgänge für Nordirland. Nordirland hat immer noch die MPs in Westminster (auch wenn nicht alle wahrgenommen werden), ist also so vertreten wie immer, egal, ob es eine Exekutive in Stormont gibt oder nicht.
Addendum: Die DUP hat vor einigen Wochen (damals als stärkste Partei) die Exekutive verlassen und damit aufgelöst. In der nachfolgenden Wahl (nicht dadurch ausgelöst) hat die DUP verloren. Die Mehrheit der gewählten Regionalparlamentarier haben kein primäres Problem mit dem Protokoll (auch wenn es keine Mehrheit für eine irische Vereinigung gibt). Ich habe dazu einige Artikel im Irlandfaden verlinkt.