LibAdwaita.
Gnome has sought to break theming for many years. Initially, they did so by changing gtk with each and every point release breaking themes, which caused themers to have to correct their themes for every Gnome Point Release. This alone drove many themers out. Horst, KillHelloKittty and so many others vanished by the wayside, fed up at having to incessantly unbreak their themes for no valid reason. @StarTreker has personally experienced just how upsetting and damaging a broken theme can be and how it can scare you at first sight. This behavior by Gnome was massively damaging to many themers reputations; as users were misled by Gnomes breakage to think that the themers were at fault for the themes breaking between point releases each few months. Or worse, many thought themers were incorporating viruses (They Were NOT).
Eventually, the stakeholders for Gnome made Gnome sign a pledge to stop breaking themes, which took effect as of gtk 3.20 (and this is why gtk themes all work the same from gtk 3.20 and up). Gnome has hmmm... more or less honored that...
LibAdwaita is a new attempt by Gnome introduced in Gnome40 (GTK4) that goes about it in a different way. It locks in all system theming to be governed by LibAdwaita, defaulting only to Gnome Supplied Themes.
If you want to use a custom theme or any other theme that suits your needs, matches your appearance or deviates from Gnome, you must seek out Gnomes permission to use your theme and have Gnome sign an Exception for it in LibAdwaita in much the same manner as having packages signed for Secure Boot on Microsoft. All Gnome needs to do is set the request aside and be "too busy" to sign the exception, claim they never received the request or that ti did not qualify for an exception. This is unbounded and unspecified as to exactly how someone is granted an exception for Gnome to permit a different from Gnome theme to be used.
Does that sound like FOSS to you?
Does that sound like the Linux you know?
Even Microsoft has not gone to such extremes on Windows.
This is unsurprising as Gnome Developers have expressed a desire to pull out of the Gnu Licensing agreement as they find it "inhibits their pursuit of their 'vision.'"
If Free Open Source inhibits a Linux Developers Vision; this raises some very hard questions about that "vision".
In addition to this, Gnomes GTK4 directly removes all support for a very large number of features that other desktop environments rely on and use. This is quite important.
Gnome has continuously removed large chunks of functionality and tool access, reducing user control. Much of this is restored in the code by independently made Gnome-Extensions which are not made by Gnome, but by users like you and me that cover for Gnome by restoring that functionality that Gnome removes.
Zorin OS 16 makes very heavy use of Gnome extensions to make Zorin OS Core usable and full-featured, rich with user controls.
Other Desktop Environments also extend the gnome base, using the provided GTK3 to patch in the features that Gnome removes.
GTK4 halts this, by removing that code from the toolkit entirely.
We can no longer use many of the facets of extensions or patch in the features from the toolkit as there is no longer anything in the gtk4 toolkit to call upon.
This undercuts the very basis of what differentiates other desktop Environments from Gnome, rendering them nearly redundant and pointless competition to Gnome, thereby setting Gnome On Top through sneaky undercutting.
Gnome validates this behavior by positing that other desktops do not align themselves with Gnomes "vision", thereby necessitating the need for Gnome to secure itself. This is akin to an abusive spouse saying that he beats his wife because she makes him hit her.
These are very real and direct actions that affect us all.
I am outspoken, often, because of the anti-FOSS behavior and unsettling direction Gnome is forcing us all into. The use of Force on users is the very antithesis of what FOSS and Linux are all about.
It's totally fine if users enjoy what Gnome has to offer as a Desktop, but that Gnome directly seeks to force itself upon us ALL truly must be met with the utmost resistance.
For many of us, we migrated away from Proprietary behavior for a reason and to have Gnome climbing that ladder and asserting it in Linux destroys what many of us hoped to achieve in leaving Proprietary systems.
Who Defends Liberty when those who live under it care not to?