User-Agent Not Updating in NSUserDefaults / WKWebView

[hsnbsst]

Description:
I’m trying to update the User-Agent in my iOS/macOS app, but it doesn’t seem to take effect. Even after setting the new value in NSUserDefaults, the web requests still use the old User-Agent.

Steps to Reproduce:
Set a new User-Agent in NSUserDefaults:

[[NSUserDefaults standardUserDefaults] setObject:@"Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/132.0.0.0 Safari/537.36 Edg/132.0.0.0"  
                                          forKey:@"UserAgent"];  
[[NSUserDefaults standardUserDefaults] synchronize];  

Expected Behavior:
The User-Agent should update immediately after restarting the app.
WKWebView and network requests should use the new User-Agent.
Actual Behavior:
The User-Agent remains the same as before.
The system does not seem to apply the changes.
Additional Notes:
I tried using registerDefaults: and setObject: but neither worked.
Restarting the app did not help.
Clearing cache with [[NSURLCache sharedURLCache] removeAllCachedResponses]; had no effect.
WKWebView.customUserAgent also does not seem to change the actual requests.