I can reproduce the issue in a similar way since upgrading to macOS 15.5. I can't access my Spring Boot backend running on localhost (just as my Angular app) but on a different port without modifying CORS rules in the backend.

The issue is likely related to CVE-2025-31205 and its fix in Webkit, see:

• https://support.apple.com/en-us/122716
• https://bugs.webkit.org/show_bug.cgi?id=290992 (publicly not available)
• https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2025-31205