Almost all of that is Mesa shaders and GTK's CPU side font-cache for GL/Vulkan, compiled CSS state, FWIW.

If you run:

GSK_RENDERER=cairo ptyxis -s

You can verify that with 69,985 here RES and 52,428 of that SHR. With 5 tabs open it jumped to 71,208 here. Presumably for the encrypted scrollback pre-allocations.

You still may not choose to use it, but it should stay relatively similar the more tabs you open.

Also, it's not a core GNOME app. It's just an app I wrote for me that the distros seem to have liked for its design/platform integration.

Thanks for writing it! I was very skeptical initially, but after using it I'm a fan. I also appreciate that I can script settings using gsettings, so I can configure it easily on new systems without having to touch the GUI (though the GUI settings are well thought out and nice to use when you don't know what you need yet).