Not available as a proper App Store app, so you have to install and run
it using Apple's beta testing option.
From
Macworld.co.uk ...
iOS 4 makes a comeback as an app
--------------------------------
Forget iOS 15. OldOS is a near-perfect recreation of Apple's
mobile operating system from 2010.
Those who feel that mobile operating systems were better in
the old days now have the opportunity to take their iPhones
back in time more than ten years by installing OldOS, which
recreates iOS 4 in the form of an app.
The OldOS app, covered by The Verge, contains numerous
fully functional apps (although not the contemporaneous
versions of YouTube and Messages) which have been rebuilt
in SwiftUI. The open-source project is the work of
18-year-old "Zane", who would have been roughly 7 years
old when iOS 4 was released on 21 June 2010.
Zane
@zzanehip
Today is Launch Day
- Introducing OldOS - iOS 4 beautifully
rebuilt in SwiftUI.
- Designed to be as close to pixel-perfect
as possible.
- Fully functional, perhaps even usable as
a second OS.
- Fully open source for all to learn,
modify, and build on.
Twitter Video: (45secs)
<
https://twitter.com/zzanehip/status/1402625414762270723>
The mobile operating system, in its official incarnation,
appeared on the original iPhone, iPhone 3G, iPhone 3GS,
iPhone 4, second, third and fourth generations of
iPod touch, original iPad, iPad 2 and second generation
of Apple TV.
iOS 4 was a significant update. It introduced folders on
the home screen, provided support for their own mobile
backgrounds, and allowed users to run apps such as audio
playback in the background. iOS 4 also introduced iBooks
on iPhone, as well as Game Center and the video-calling
app FaceTime.
OldOS is available via Apple's TestFlight beta test
service, and it's on GitHub.
TestFlight:
<
https://testflight.apple.com/join/67C9v9VB>
GitHub:
<
https://github.com/zzanehip/The-OldOS-Project>
<
https://www.macworld.co.uk/news/ios-4-oldos-app-3805506/>