Themes for Wordpress are often bloated and overloaded with a lot of scripts, Jquery and big CSS files. Fortunately modern themes for Wordpress try to achieve good results regarding speed and performance. And there are also projects and initiatives like SustyWP which are going into an extreme minimal way to get the fastest possible theme for Wordpress. SustyWP is a free Wordpress theme which is extremely lightweight and is able to deliver Wordpress in only 6KB.
The scope of the project also has climate and sustainability in mind as the average website transfers megabytes of data today and impacts the internet carbon footprint.
Link to SustyWP Github Repository Github Link