<input> accept Attribute in Microsoft Edge

"accept" attributes are definitely not supported in Microsoft Edge at this point. I confirmed your behavior as "no go" in edge, but showing up in IE via the [...] thing in the upper right of Edge.

The Edge status shows it as "Under Consideration" with just 198 votes at https://wpdev.uservoice.com/forums/257854-microsoft-edge-developer/suggestions/13661175-full-spec-support-for-accept-in-input-type-file .

If you're interested in implementation of the HTTP Client Hints (aka "accept") on Edge be sure and vote it up at the URL above.

As @mparizeau reported, @JoeHealy's answr is about HTTP Accept header, which is not what the question is about.

To answer the question: at the moment, Edge does not support accept on <input type="file" />.

There used to be a bug tracker here, now it's just a SO redirected search -_-. Anyway, with the upcoming new Microsft Edge (Chromium) this issue will be resolved.