The linked RFE removes the JVMCIUseFastLocking symbol and it was backported to Lilliput 21 repository. The patch was NOT backported to JDK21.
Graal23 community still refers to that symbol, though [1]. However, since the symbol was removed the flag will be silently set to `false` in GraalJIT. The flag being false causes this intrinsic [2] to use LM_MONITOR as locking mode, however JDK21 uses LM_LEGACY as the default locking mode.

I propose to put the flag back and set its value according to the value of the LockingMode option [3].

[1] https://github.com/graalvm/graalvm-community-jdk21u/blob/master/compiler/src/jdk.internal.vm.compiler/src/org/graalvm/compiler/hotspot/GraalHotSpotVMConfig.java#L119
[2] https://github.com/graalvm/graalvm-community-jdk21u/blob/master/compiler/src/jdk.internal.vm.compiler/src/org/graalvm/compiler/hotspot/replacements/MonitorSnippets.java#L868
[3] https://github.com/openjdk/lilliput-jdk21u/blob/lilliput/src/hotspot/share/runtime/globals.hpp#L1983