See 2.5.6 here: developer.apple.com/app-store/review/guidelines/

It is possible to build perfectly decent web apps but many times they choose not to or it’s too much trouble

On iOS, they quite literally can’t in some aspects. They’re restricted to using the supplied WebKit Apple enforces. On Android you can use the Blink Web View (Chromium) or Gecko Web View (Firefox). Both of which can be bundled in the app, or you can use the system version.

They have different browsers with limitations but I don’t know about not proper.

Every single iOS “browser” is WebKit. AKA Safari. Due to Apple’s plug-in system being proprietary, it’s difficult to extend. Third party browsers typically use JavaScript injections which slow down the browsing experience.

You’re not actually using Microsoft Edge. You’re using Safari and it’s being identified as such by the UA string. Due to Safari being in last place for web standards feature support, it’s not surprising you’re coming across the issue.