In Plasma 5.20 and later, the circle is automatically removed when you disable it in System Settings > Window Decorations > Breeze > Click the pencil icon > uncheck "Draw a circle around the close button"

(In reply to Nate Graham from comment #1)
> In Plasma 5.20 and later, the circle is automatically removed when you
> disable it in System Settings > Window Decorations > Breeze > Click the
> pencil icon > uncheck "Draw a circle around the close button"

I already did that and it works for the normal Breeze Dark for qt,but it doesn't work for gtk

Works for me. If you change your window decoration theme to something else, do the button icons in GTK apps change?

(In reply to Nate Graham from comment #3)
> Works for me. If you change your window decoration theme to something else,
> do the button icons in GTK apps change?

no,they don't.

OK, so that's the problem. The window decoration you choose for KDE apps is supposed to get synced with GTK headerbar apps.

What version of Plasma are you using, and what window decoration theme are you using? Can you attach a full-screen screenshot that shows at least one KDE app window and one GTK headerbar app window, with their window decoration buttons being mismatched?

Also, please tell if the GTK app is installed via flatpak/snap or not. Because if the GTK app is installed via flatpak (or snap), it won't work.

(In reply to Nate Graham from comment #5)
> OK, so that's the problem. The window decoration you choose for KDE apps is
> supposed to get synced with GTK headerbar apps.
> 
> What version of Plasma are you using, and what window decoration theme are
> you using? Can you attach a full-screen screenshot that shows at least one
> KDE app window and one GTK headerbar app window, with their window
> decoration buttons being mismatched?

Here my full system information:
https://i.imgur.com/65nlqHy.png
Here the screenshot you want:
https://i.imgur.com/cItMB5U.png

The theme I'm using is Breezr-Dark and I installed the programs I used in the screenshot from the official repo,I don't have Flathub/Snap programs.

There was a fix, that was merged in Plasma 5.20.5, that touches the GTK CSS updating mechanism. Please update to the latest Plasma version and check if the bug persists.

(In reply to Mikhail Zolotukhin from comment #8)
> There was a fix, that was merged in Plasma 5.20.5, that touches the GTK CSS
> updating mechanism. Please update to the latest Plasma version and check if
> the bug persists.

I updated and still have that bug

Hm, strange, it works for me. I've tested that on KDE Neon 5.20.5 (my local machine) and on master (KDE Neon Unstable in the VM). Maybe someone other can reproduce.

What's interesting is that you cannot have Breeze-Dark theme, because its selection in GTK System Settings page cannot be performed (the theme is hidden). What is actually selected in the GTK page in your settings?

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(In reply to Mikhail Zolotukhin from comment #10)
> What's interesting is that you cannot have Breeze-Dark theme, because its
> selection in GTK System Settings page cannot be performed (the theme is
> hidden). What is actually selected in the GTK page in your settings?

I downloaded a GTK theme called "Breeze Dark GTK",isn't that the way how I should use it?

How did you download it? From where?

(In reply to Nate Graham from comment #13)
> How did you download it? From where?

I go to System Settings>Application Style>Configure Gnome/GTK Application Style>Get new Gnome/GTK Application Styles,then download the theme Breeze-GTK (https://store.kde.org/p/1197982) and then select the GTK theme "Breeze-Dark-GTK".

We don't touch 3rd party GTK themes. Because of that the circle change won't work. 

To properly disable the circle you need to set your GTK theme to "Breeze" (without any suffixes and prefixes), then select Breeze Dark color scheme in Appearance > Colors. That way you will be using the official Breeze GTK theme, that grabs its appearance from various Plasma settings, like colors and window decorations.

(In reply to Mikhail Zolotukhin from comment #15)
> We don't touch 3rd party GTK themes. Because of that the circle change won't
> work. 
> 
> To properly disable the circle you need to set your GTK theme to "Breeze"
> (without any suffixes and prefixes), then select Breeze Dark color scheme in
> Appearance > Colors. That way you will be using the official Breeze GTK
> theme, that grabs its appearance from various Plasma settings, like colors
> and window decorations.

Is the default Breeze GTK theme pre installed?

Yes. If not, it is called "breeze-gtk" in pacman.