Font settings of the code block

Hi

You can make site wide changes to any block, including the code block by opening the Styles panel in the Site Editor and selecting the Blocks panel.
See https://www.ads-software.com/documentation/article/styles-overview/#blocks

In theme.json, the code block is styled on line 242, the style variations have its own styles.
https://github.com/WordPress/wordpress-develop/blob/trunk/src/wp-content/themes/twentytwentyfive/theme.json#L242

Remember that if you edit the files directly you will loose your changes if you update the theme.