Sorry for the brevity @Zeke8990. I don’t recall a time where responsive images were ever generated on a page where images came from a CMS field. I may have assumed that the blog post was simply incorrect (it’s from 2016). Many blog posts are from third parties, yet this one is not. I have avoided using the CMS with anything but small images unless I handled the images externally from Webflow (which I do mostly when I use it).
The related page on the University references the blog and does not clarify whether CMS generated assets (inline not rich text) indeed trigger the responsive image generation.
In the University they state;
What are the supported image types?
This feature generates responsive variants for all inline JPGs and PNGs, except those added via rich text elements. It also doesn’t apply to background images. We recommend SVGs and PNGs for high detail or vector based images, since these have lossless compression.
What I can confirm.
Images from the asset manager, placed on pages and even collection templates, trigger the responsive image generation we would expect.
Images that are derived from CMS collection image fields do not, regardless of where (collection template or collection list).