Then you best stay away from THREE and any MVNO that uses them. This outage affected all networks that use the THREE network to provide a service.
I have a Vodafone eSIM as a backup line on my iPhone (Pay Monthly) and they had an outage not long ago too. Things break, such is life. But then I am only paying SMARTY a tenner for 120GB of 5G data with unlimited calls, so I can live an outage or two every few years. (FYI - I only get 6GB of 4G data with unlimited calls with Vodafone)