https://gitlab.gnome.org/GNOME/gtk/-/blob/main/NEWS?ref_type=heads
GTK is a multi-platform toolkit for creating graphical user interfaces.
I know this is good but don't know why.
can someone explain the advantage of using vulkan?
OpenGL is the only other open source alternative. Vulkan is developed by the folks who created and manage the OpenGL specification. (https://www.khronos.org/) To shorten the list of differences I will specify one. OpenGL is ancient and can not compete on modern hardware. Vulkan is the new hotness that everyone in the future will support.
There are a many reasons that more fully answer your question but this is the short/fast.
I think it's more that opengl is a higher level API that offers less granular control in exchange for easier cross platform support.