We should remove the code in UserAgentIOS.mm that reads an override UA from the NSUserDefault [com.apple.WebFoundation UserAgent]. It is incompatible with the modern need to compose the UA from various bits of information these days (e.g. desktop vs. mobile). Clients should use the API to set the application name or UA instead. I have stumbled upon one client (com.fark.hey), and there are likely others, so it should be a linked-on-or-after change.
I left a reference here next to the code in https://trac.webkit.org/changeset/268697/webkit
<rdar://problem/70699433>
Just to update that this FIXME is still present: https://github.com/WebKit/WebKit/blob/6ead5274db5f92656360fa1fbae3e0091481fc4f/Source/WebCore/platform/ios/UserAgentIOS.mm#L90
Pull request: https://github.com/WebKit/WebKit/pull/14805
Committed 265034@main (6a68b0c65d6c): <https://commits.webkit.org/265034@main> Reviewed commits have been landed. Closing PR #14805 and removing active labels.