Is iOS still based on macOS? [closed]

No, and yes at the same time. They share the XNU kernel and some of the core libraries.

The XNU kernel was the kernel of NextSTEP and is used as the foundation for tvOS, iPad OS, iOS, and macOS. This means that they do share common traits and originally iPhone OS (now iOS) was an adaptation of macOS for a phone with "minimal^" changes.

Today the kernel remains shared and changes from relevant for iOS but comes initially from macOS is "simply" used in iOS but the same is true in the other direction. So where in the beginning iPhone OS was based on Mac OS X now it is more a symbiotic relationship.
As an example getting macOS to run on M1 was much easier as they (probably) could reuse a lot of the XNU kernel drivers originally developed for iPad OS / iOS.

^minimal: There were introduced a lot of code to the source tree to support the new chips and for instance LTE capabilities.

After a lot of search, I found a great explanation :

iOS is fork of Mac OS X according to Steve Jobs in 2007 Apple event :

Today, we are going to show you a software breakthrough. Software that is at least 5 years ahead on what is on any other phone. Now how did we do this? Well, we started with a strong foundation — iPhone runs OS X. Why would we want such a sophisticated operating system on a mobile device? Because it is got everything we need.

Apple called this operating system iPhone OS, and then iOS. But iOS and macOS use the same Unix-based core named "Darwin" as well as many frameworks. The watchOS and the tvOS also run variants of iOS that also rely on Darwin.

iPhoneOS didn't became iOS. It is just a nick name. less text nothing else. Also iOS is based on macOS but since it is introduced in 2007; the design has changed but the Kernel (Core Idea) still same.

Each Apple operating system is based on Darwin and then Apple optimize the interface so it works perfectly for each device, so it looks different and works great for each Apple device.

Darwin is the core operating system that all Apple operating systems are based on.

Darwin is:

• Free
• Open Source
• UNIX
• Based on BSD (FreeBSdD, OpenBSD, NetBSD, etc.)
• Descended from NeXTStep

Darwin is the starting point for:

• macOS: MacBook, Mac Mini, iMac
• iOS: iPhone
• iPadOS: iPad
• watchOS: Apple Watch
• tvOS: Apple TV
• audioOS: Apple HomePod

Some of Information are in Wikipedia.