All photo media reduced to 300px wide

[jkorchok]

I've tested with several WordPress themes plus my own to make certain this is a core problem.
My site (brandwares.com) uses fluid design to fit a multi-column design to the browser width. I've ported this to my WordPress theme.
When I add media (almost always a screenshot), I set the picture width to 100% so the picture fills the width of my fluid layout columns. WordPress over-rides this with:
sizes="(max-width: 300px) 100vw, 300px"
The result is a 300 pixel wide downsampled image that either doesn't fill the column width in my theme or fills the width with a blurry image in Twenty Sixteen, Twenty Seventeen, Twenty Nineteen and Twenty Twenty.
Here is a sample page that shows a screen shot mangled by WordPress: ​http://www.brandwares.com/bestpractices/2020/07/ooxml-hacking-protected-area-exceptions-word/
Neither result is acceptable. I am not going to spec a picture width in pixels, because that is bad practice in a fluid design. When I spec 100% width, I expect the picture to be 100% width at full resolution. Please fix this glaring defect and stop making your own private version of HTML on my site.

[Otto42]

This is meta Trac, where we track issues about the WordPress.org site and related properties.

You should post your issue on the support forums, or on the core Trac if you have found a bug.