It has now emerged that after being informed that Safari was likely to fall under the DMA's regulations, Apple filed formal a response to the European Union claiming that Safari is, in fact, "three distinct web browsers." The company's claim is based on the argument that Safari for iOS, iPadOS, and macOS are entirely different and serve different purposes.
On example cited by Apple is Safari's sidebar feature on iPadOS and macOS, allowing users to see opened tabs, tab groups, bookmarks, and browsing history. Since this feature is unavailable in the version of Safari for iOS, Apple claimed that it is a distinctly different browser. The company added that each version of Safari serves different purposes for users depending on the device upon which it is accessed.
The European Commission went on to point out that Safari's functionality and underlying technologies are near-identical across platforms. The Commission even highlights Apple's own marketing materials for its Continuity feature, which appear to contradict the company's claims, touting the tag line "Same Safari. Different device." As a result, the Commission rejected Apple's claim and insists that "Safari qualifies as a single web browser, irrespective of the device through which that service is accessed."
All Linux distos use the same kernel, are they all the same?
The Linux kernel isn't in a position that it can manipulate the market through imposed standards. For most Linux distros their distribution and installation is controlled by the end user. There isn't a default distro - except for pre-installed which is marginal.
The user of a Linux distro has a choice in the one they choose. They actively have to seek it out in most cases. So they impart agree to the UI, default apps and package management system.
Where as people buying windows, apple, android and chrome os. Are presented with a default browser and in either can't or are heavily discouraged from choosing an alternative. Users may also have to use a certain browser to access a website, which happens with chrome.
The types of user are also different.
Again this doesn't become relevant unless an operating system is in a position to exploit (and has ambitions or has exploited) its large/monopolistic market share. The Linux kernel hasn't approached this. Not even in the server market, as Microsoft remain a powerful player and the operators are highly informed non commercial users.
What makes the distinction on linux distro's is the package manager, you could make the argument that Debian and Ubuntu are the same but you cannot make the same claim about Slackware and Arch.