This is more like supporting AVX512 than a whole separate architecture. If you have to target both old and new devices from one binary, you do a runtime feature check and call the corresponding code.
That is certainly more code, but not double. You only need it for the parts of the code that are both (a) bottlenecks worth optimizing and (b) actually benefit by using the new instructions.
In games, perhaps. In basically nothing else though. And I have 0 games on my M1, yet my apps folder is 23 GB. Docker, Edge, and SketchUp all 2+ GB, despite not having almost any UI to speak of.
(Edit to remove iMovie from the list, as it has GB's of "Transitions" and "Titles" that I really should just delete)
All three examples you gave have substantial UI and other bundled assets. For example, the Docker Desktop app is about 2GB on my computer, yet included assets make up at least 1.2GB, and a further 600MB is a bundle containing the UI, which itself is about 100MB of binaries.
If you actually open those bundles (as they're called on macos) and take a look inside, you'll see that they don't even contain all of their assets, anyways, often linking to frameworks contained in ~/Library
This is a very layperson explanation, btw, but I assure you that "in modern desktop software, code is a tiny bit of the total size of the application" is a very true statement.
There are cases where the app icon is larger than the compiled code in some apps and if you include a couple images for things like “here is how you give my app access to record the screen” that can also account for a large part of your app bundle.
Yes, game assets really take it to another level but it’s been my experience that even apps without a lot of UI still have their images making up a lot of the app bundle size.
That is certainly more code, but not double. You only need it for the parts of the code that are both (a) bottlenecks worth optimizing and (b) actually benefit by using the new instructions.