There is not a universal sidebar for Hugo themes, since each theme has its own layout and CSS (from scratch, Bootstrap, Tailwind and so on). I think the best way is to request a feature from the target theme’s author if you aren’t familiar to Hugo theme development.
AVIF (based on AV1/VP10) is a really good format for web images (highly compressed) and is supported by most browsers, even Apple - that dislikes open-source formats - embraced it last year.
JXL is great for high quality photography, but browser support is poor.
WebP is a really bad format (based on VP8), most times it’s even worse than JPEG (with MozJPEG encoder). I stopped using it on Wordpress years ago.