Mozilla is unhappy because the use of browser engines other than WebKit will be restricted to the EU, forcing them to develop two different apps.
For an independent browser like Firefox, managing two browsers is not easy, so it can be forgiven that this could be seen as almost harassment.
Also, the fact that the use of browser engines other than WebKit is limited to iOS means that the use of WebKit is still forced on iPadOS, which also increases the effort for Mozilla.
You asked what parts aren't compatible, and one answer is everything bought for Apple computers, iPhones, iPads, etc. Apps, media, anything that isn't subscription based.
I (and other people) have already said that re-buying the same products and learning alternative ones is expensive in both time and money. That's the point.
And I don't know a ton of iOS killer apps but you would probably have to convince people with a ton of effort that Procreate is replaced by something on Android, let alone any other app I don't know about
Ok? And Photoshop license isn't for just osx... you're literally proving the point that you can migrate but you don't want to because of some stupid allegiance to apple
I... Don't like Apple at all. I'm engaging in a thing called a thought experiment, which is required to rationally assess why somebody might not want to throw away things they have purchased and devote both more time and more money to something that doesn't work as well as it.
So I don't know what all the cool killer Mac apps. Replace Photoshop with the name of a bunch of cool killer Mac apps, and repeat the question.