>many apps now just use CSD
If there's something I hate about Linux, it's CSD (Client-Side Decorations, in case people don't know what it is).
If I wanted all my apps to look different from each other, I'd use macOS. I want a clean desktop environment, with predictable window frames that are customizable and they all look the same. CSD destroys that.
Conversely, I don't want all of my apps to look identical to each other. I want to be able to tell with a submoment of a glance what app I am working on or looking for without having to cognitively engage to locate it, breaking my state of flow in the process.
You're defeating your own point. CSD in practice breaks a basic feature of the desktop : knowing at first glance which of the windows will receive whatever you type on the keyboard.
For eons the standard was: the only one with the title bar showing the theme accent color. That is consistent, predictable, keeps the user in the flow.
With CSD each app does whatever inconsistent thing they can fancy. You type and oops deleted something in the wrong window.
Alas now even many default SSD setups fail at this (selected and non-selected windows look pretty much the same) and keyboard-first workflow is much hindered.
Linux doesn't mean GNOME.
KDE favors server-side decorations.
I mean, most apps I use daily, no matter the OS, have CSD. Teams, Spotify, Slack, Firefox, Postman, IntelliJ etc...
Doesn't matter which OS they all have different styles. I can understand it's not liked by everyone, but that ship has sailed and no "big" app will use SSD anymore.
Having no CSD at all is unacceptable on small screens IMHO, far too much real estate is taken up by a title bar, you can be competitive with SSD by making them really thin, but then they are harder to click on and impossible with touch input. At the moment I have firefox setup with CSD and vertical tabs, only 7% of my vertical real estate is taken up by bars (inc. Gnome), which is pretty good for something that supports this many niceties.