Summary of me looking at the app for about 20 minutes:
Having subscriptions as it’s own tab is confusing as hell to me and leads to a weird UX as the UI first needs to switch to the posts tab before triggering the navigation there. This results in a harsh change of the content followed by the pushing of the new screen. Took me a while to realize what was happening as I thought there was a bug that added images to the subscription rows as this happens fast enough to not make you realize you are seeing Posts/All for a split second.
All/local/… does not react to changes in the set post style. Pull to refresh will not help. Only switching via the Navigation Bar menu will update the post layout.
While we are at it. A preview for this setting would be great.
Switching to the account tap will always return you to the first screen and not the sunscreen you were on previously. At least that problem does not exists for posts.
Guests instances could really use an explanation about what they do.
The NavigationBar is very not iOS like.
The back button should have a meaningful label and having no title until you scroll feels wrong. I think you are trying to emulate the butchered detail view of the mail app, but without the back button text this just feels empty but adding it might be enough to make it work.
Also there is a UI bug when the navigationBar (dis)appears where the back button vanishes first/gets added before the bar appears.
Tapping next to the comments count beneath the post sometimes collapses/expands the post. Sometimes not.
Sorry if I sound a bit harsh. I see a lot of potential in this app. But also a lot of work.
Onboarding is pretty great though.