Local file iframe requests remain stalled in Microsoft Edge 156.0.4314.42 but work in Chrome, Firefox, IE mode, and localhost

After updating Microsoft Edge to version 156.0.4314.42 (Official build, 64-bit), my local HTML tool can no longer load child HTML pages through relative iframes. The parent HTML file and three child HTML files are stored in the same locally synchronized OneDrive folder. The iframe paths are relative.

When the parent HTML file is opened directly in normal Edge mode through a local file:// URL, all three iframe requests remain stalled. In Edge DevTools, the requests show:

• Transferred size: 0 B
• No status code
• No response headers
• Timing stops at “Stalled”
• “Provisional headers are shown”
• No iframe load or error event is triggered
• No error appears in the Console

The following tests have already been completed:

• Each child HTML file opens normally by itself in Edge.
• The same parent page and iframes work normally in Google Chrome.
• The same parent page and iframes work normally in Mozilla Firefox.
• The page works in Edge IE compatibility mode.
• The page works in normal Edge mode when served through http://localhost.
• OneDrive confirms that the files are fully synchronized.
• No relevant URLBlocklist, file:// restriction, or iframe-blocking policy was found in edge://policy.

The issue therefore appears to occur only when normal Edge Chromium mode loads child HTML files through local file:// iframes.

Could you please confirm:

1. Is this a known issue or regression in Edge 156?
2. Has Edge changed the handling of local file:// iframe navigation?
3. Is there a supported policy, setting, or workaround that allows local iframe pages to load without using IE mode or a local HTTP server?
4. Will this behavior be addressed in a future Edge update?