Hello,
Thank you very much for choosing our theme and for contacting us.
You can change the font by means of Advanced typography option, which allows to choose the item from a drop-down or insert your custom CSS class. Please navigate to the Theme Settings > Typography > Advanced Typography.
Here is the documentation providing more detailed instructions: https://xtemos.com/docs/basel/advanced-typography-settings-2/
Your menu applies two types of drop-downs: Mann uses Mega menu blocks https://xtemos.com/docs/basel/create-menu/ and https://xtemos.com/docs/basel/html-blocks/ as you see Mega menu blocks are created in HTML blocks and you can add an image by means of WP Bakery page builder element.
Kids menu item applies the default WordPress menu that is why different styles are applied.
Best Regards