RSS Feed in IE 11 shows error - Feeds with DTDs are not supported in SharePoint 2016.

It was working till yesterday.
RSS Feed in IE 11 shows error - Feeds with DTDs are not supported in SharePoint 2016.

It was working till yesterday.
Whether all RSS feeds or only this RSS feed occur the error?
Have you updated or made some changes for SharePoint in the past few days?
I suggest you clear browser cache then have a test. Or open RSS feed in another browser, compare the result.
And you could go to ULS logs to find more clues.
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