I also faced the same problem. After some Googling, I did not find a solution, but I understood why it was happening:
UIApplication.openURL(
has been deprecated since iOS 10 and replaced by the more robust UIApplication.open(:options:completionHandler:).
Newer iOS versions (e.g., iOS 18) are enforcing this deprecation more strictly, causing the warning and potentially preventing the deprecated method from functioning as expected.
I came up with an idea to create a custom C++ node which would fix the issue, but I don’t know C++. So, I asked AI to do that for me and it worked lmao 
At the end of the day I converted that node to plugin. Here’s the download link: IOSURLLauncher.zip - Google Drive
Just drop it inside your ProjectName/Plugins folder. Its BP implementation looks like this:
The node checks if current platform is iOS and outputs a bool value. Thus, if not then just use a regular Launch URL node so it could launch on the rest of the platforms.
Also, leaving the link for the whole conversation with Gemini just in case. The interesting part starts after the give me c++ code for the node prompt: https://g.co/gemini/share/38dad8e989d1
Hope this helps