High cpu usage when I run sample application form gtkmm4

Hi,
I am using ubuntu 22 os and gtkmm4. I got the source code from this gtkmm4 tutorial.
When I run this application, using the “$ top” command I observed high CPU usage, and its keeps on increasing whenever I hit that button. is this the behavior expected with GTKmm4 and why this much CPU usage for such a simple application?