I'm not a lawyer but I think Xerox had the same question back in '89 [1]. Given Apple's luck in pursuing infringement claims against Microsoft [2], I doubt a copyright suit would be fruitful in this case.
[1] https://www.nytimes.com/1989/12/15/business/company-news-xer...
[2] https://legal.thomsonreuters.com/blog/1988-apple-sues-micros...
https://forums.theregister.com/forum/all/2021/02/12/freebsd_... was thought to be a joke …
https://149366088.v2.pressablecdn.com/wp-content/uploads/202...
Not sure what "open-source Linux community" means to you, besides a phrase that can be used to denigrate and diminish the work of people who have skill and vision by associating them with unrelated projects that lack polish.
You're also doing a pretty annoying thing where, rather than engaging with someone on the topic of discussion, you instead appeal to the audience's intuition and essentially suggest that the conversation need not happen because the other side can be dismissed outright due to Common Sense things that everyone Knows. (It's a great tactic when your goal is to prevent anyone from taking something seriously because serious examination would necessarily lead to confronting something uncomfortable.)
Anyway, here is gnome 3:
https://external-content.duckduckgo.com/iu/?u=https%3A%2F%2F...
here is big sur:
https://cdn.osxdaily.com/wp-content/uploads/2020/06/macos-bi...
Let's take a look at one of the most shown off redesigned apps
Here is Mail.app (sierra to catalina):
https://external-content.duckduckgo.com/iu/?u=https%3A%2F%2F...
Here is Mail.app (Big Sur):
https://i1.wp.com/morrick.me/wp-content/uploads/2020/08/defa...
Here is Gnome's mail app (predates big sur by several years, even in this incarnation):
https://wiki.gnome.org/Apps/Geary?action=AttachFile&do=get&t...
So, Gnome's design and Apple's didn't exist in a vacuum. I'm not saying Apple told someone to go rip off Gnome 3, or that Gnome 3 is just better than Big Sur in some way. But I think it's altogether too harsh to deny it had any influence when we look at the changes from Catalina to Big Sur.
I don't think anyone would say design exists in a vacuum, nor that the open source community has no ideas that Apple or other companies would consider -- I mean, look at CUPS and KHTML! But open source has, well, not historically been great with its desktop UX design. The best free software interfaces that I see tend to take pretty direct cues from (hopefully well-designed!) commercial counterparts; more often than not deviations from those established norms make things worse rather than better.
CUPS and KHTML existed far before Apple borrowed them.
That would be why I cited them as examples of open source ideas Apple would consider. :)
The best I've come up with is the switch from a two row title bar/header to a one that is integrated into just one row. Which could very well be inspired by Gnome 3 or parallel evolution.
Are there other UI elements that I should be seeing in Big Sur that look like they have inspiration, homage, blatant copying that I'm not seeing here?
To my eye they have a somewhat similar aesthetic but and general layout but their differences are many when looking closer.
Calling it a "dumpster fire" is a bit overdoing it when it's just a different paradigm.
I am attacking the paradigm. It has had its time. It is done. It should leave.
[1] https://github.com/eczarny/spectacle https://github.com/rxhanson/Rectangle
My preference would be to keep it as is but have window switching work like app switching. The separate order in which the two cycle is a pain.