Routing/mobile layout question

[THOUSAND-SKY]

Assume you'd have a layout like in this example, https://remix.run/docs/en/main/guides/errors#nested-error-boundaries , on mobile you'd have to hide everything except the "Something went wrong" block. Is this the way responsive design is generally done, with SSR? useLocation or useMatches and then hide content that doesn't match the leaf (on mobile)?

I used to hear "start from mobile, lazily expand toward desktop," but I don't see a clean way of doing that on SSR, unless I start matching user-agent (which I'd rather avoid I guess).

This is the example layout in question: