By any chance there is any option to make the featured images on blog posts go full width? Or at least could I chose the size on the blog post pages?
Something like the image attached.
I hope you are well today and thank you for your question.
To achieve this, you have to develop custom code in the child theme of Jevelin theme.
Developing custom code for custom functionality is beyond the scope of support that we provide here. Please see https://themeforest.net/item/jevelin-multipurpose-premium-responsive-wordpress-theme/14728833/support
If you are not a developer then you can consider hiring a developer to develop it for you. You can hire a developer from any freelance site. Shufflehound recommends the developer https://www.upwork.com/freelancers/~011652ffec8865c6d5