I am facing the same issue, I was using a similar approach (using fetch instead of XMLHttpRequest) to get the blob. It works in iOS 12 and 13 but is broken in iOS 14. It appears that a change in iOS 14 has broken the ability to download blob resources when using WKWebView. Here is a link to the approach that uses JS fetch: https://developer.apple.com/forums/thread/108394?page=1#653466022 Is there a way to get a blob resource when using WKWebView in iOS 14? Does anyone have a fix for this?

This approach was working for me in iOS 12 and 13. It is broken and does not work in iOS 14. In iOS 14 I see the following error in the logs: error: fetch threw, error: TypeError: The operation couldn’t be completed. (WebKitBlobResource error 1.), url: blob:https:yourbloblink Has anyone else encountered this? Does anyone have working code or a solution for iOS 14? I am unable to download and display PDF blobs in iOS 14 via WKWebView.