YSK: You can see which instances your home instance is federated with and which they've defederated/blocked by going to "/instances"
For example, you can see this breakdown for Lemmy.world by going to https://lemmy.world/instances
Mlem - iOS App for Lemmy (testflight.apple.com)
FYI, Lemmy and Kbin are Progressive Web Apps, meaning you can install them as regular apps to your phone's home screen
On iOS: tap the share button in browser => add to home screen...