how can you tell if someone blocked you on iphone

Focus mode at least tells on itself. If they have it on you usually get a line saying they have notifications silenced, and you don't get that when you're blocked. The real tell is time. No Delivered for days while you can see them active elsewhere, and calls that go to voicemail every single time, not just once.

There's no notification for it. iMessages that never say "Delivered" plus calls going straight to voicemail is the usual sign, but a phone that's off or on a focus mode looks identical.