First clone this repo with --recurse-submodules option.

Then, you will need to apply labs-openjdk/ios-jdk.patch to labs-openjdk-21 submodule.
Setup a boot jdk (it is a JDK used when building the ios JDK). You can set it up by fetching one or simply download GraalVM 23.1.3 and set your JAVA_HOME environment variable to it.
To fetch a boot JDK execute:
mx -y --no-warning fetch-jdk --java-distribution labsjdk-ce-21 --to pathwhereyouwanttosetbootjdk --alias jdk21. Then in labs-openjdk-21 submodule run configure command:

./configure
    --with-conf-name=labsjdk
    --with-version-opt=jvmci-23.1.3-b33
    --with-version-pre=
    --with-vendor-name="GraalVM Community"
    --with-vendor-url=https://www.graalvm.org/
    --with-vendor-bug-url=https://github.com/oracle/graal/issues
    --with-vendor-vm-bug-url=https://github.com/oracle/graal/issues

Then run make CONF_NAME=labsjdk graal-builder-image.
Once done, it should have generated all sources and headers needed to compile java static library for iOS.
To compile java static library for iOS open svm.openjdk.xcodeproj and compile static library.
When compiled you should have libjava.a ios static library in xcode build output folder.

Then you will have to build SVM static library.
To do so open svm.graal.xcodeproj and compile it for iOS.
When done, you should have a libjvm.a static library in xcode project build output folder.

You can then include both libjava.a and libjvm.a static libraries in your native app to enable java for your iOS app.