Offline fallback page with service worker
Years ago, I did some research into how native applications responded to a lack of network connectivity. Whilst I’ve lost the link to the analysis (I could swear it was on Google+), the overarching narrative was that many native applications are inextricably tied to the internet that they just straight up refuse to function. Sounds like a lot of web apps, the thing that set them apart from the web though is that the experience was still ‘on-brand’, Bart Simpson would tell you that you need to be online (for example), and yet for the vast majority of web experiences you get a ‘Dino’ (see chrome://dino).