TL;DR: This is likely a temporary issue that will resolve itself when the next iOS 17 Beta SDK is available.
If you look at Source/***/***/PlatformHave.h
, it uses a header check in addition to an SDK version check:
#if ((PLATFORM(MAC) && __MAC_OS_X_VERSION_MAX_ALLOWED >= 140000) \
|| ((PLATFORM(IOS) || PLATFORM(MACCATALYST)) && __IPHONE_OS_VERSION_MAX_ALLOWED >= 170000) \
|| (PLATFORM(WATCHOS) && __WATCH_OS_VERSION_MAX_ALLOWED >= 100000) \
|| (PLATFORM(APPLETV) && __TV_OS_VERSION_MAX_ALLOWED >= 170000) \
|| PLATFORM(VISION))
#if __has_include(<Network/proxy_config.h>)
#define HAVE_NW_PROXY_CONFIG 1
#endif
#endif
But the method declaration above doesn't include this check (because it's a public header).
You can workaround this issue by doing something like this before including WebKit headers (UNTESTED):
#include <os/object.h>
#if !__has_include(<Network/proxy_config.h>)
OS_OBJECT_DECL_CLASS(nw_proxy_config);
#endif