Thanks @Softsal for posting and @snowak for answering. This is very sad that ApplicationCache is disabled when ServiceWorker is still not available in WKWebView on iOS15. My web view based app lost the instant open experience. That reminds me that "benevolent neglect" was used to describe Apple's attitude to the Web. When they cannot offer more to native apps, they take away existing things from the Web.

Annoying. Same here. Seems a bug took 7 month to have someone look at. Is user privacy focusing still Apple's top strategy?