I found several tests failures run with TEST_THREAD_FACTORY=Virtual

1. These tests fails on linux-x64 with default VM option and with release jdk binary which build from loom-repo:
jdk/internal/misc/VM/RuntimeArguments.java
runtime/Dictionary/ProtectionDomainCacheTest.java
runtime/classFileParserBug/TestEmptyBootstrapMethodsAttr.java
runtime/logging/LoaderConstraintsTest.java
serviceability/jvmti/events/Breakpoint/breakpoint01/breakpoint01.java
serviceability/jvmti/events/ClassLoad/classload01/classload01.java
serviceability/jvmti/events/ClassPrepare/classprep01/classprep01.java
serviceability/jvmti/events/MethodEntry/mentry02/mentry02.java
serviceability/jvmti/events/MonitorWaited/monitorwaited01/monitorwaited01.java
serviceability/jvmti/negative/thrinfo02/thrinfo02.java
serviceability/jvmti/thread/GetThreadInfo/thrinfo01/thrinfo01.java
serviceability/jvmti/vthread/ContinuationTest/ContinuationTest.java
serviceability/jvmti/vthread/FollowReferences/VThreadStackRefTest.java#default
serviceability/jvmti/vthread/SelfSuspendDisablerTest/SelfSuspendDisablerTest.java#default
serviceability/jvmti/vthread/SelfSuspendDisablerTest/SelfSuspendDisablerTest.java#no-vmcontinuations
serviceability/jvmti/vthread/SuspendResume1/SuspendResume1.java#default
serviceability/jvmti/vthread/SuspendResume1/SuspendResume1.java#no-vmcontinuations
serviceability/jvmti/vthread/SuspendResume2/SuspendResume2.java#default
serviceability/jvmti/vthread/SuspendResume2/SuspendResume2.java#no-vmcontinuations
serviceability/jvmti/vthread/SuspendResumeAll/SuspendResumeAll.java#default
serviceability/jvmti/vthread/SuspendResumeAll/SuspendResumeAll.java#no-vmcontinuations
serviceability/jvmti/vthread/VThreadTest/VThreadTest.java
serviceability/jvmti/vthread/WaitNotifySuspendedVThreadTest/WaitNotifySuspendedVThreadTest.java
vmTestbase/nsk/jdi/ObjectReference/referringObjects/referringObjects003/referringObjects003.java
vmTestbase/nsk/jdi/stress/serial/heapwalking001/TestDescription.java
vmTestbase/nsk/monitoring/MemoryUsage/from/from001/TestDescription.java
vmTestbase/nsk/monitoring/ThreadInfo/from_c/from_c001/TestDescription.java
vmTestbase/nsk/monitoring/ThreadInfo/getLockName/getlockname001/TestDescription.java
vmTestbase/nsk/monitoring/ThreadInfo/getLockOwnerName/getlockownername001/TestDescription.java
vmTestbase/nsk/monitoring/ThreadInfo/isInNative/isinnative001/TestDescription.java
vmTestbase/nsk/monitoring/ThreadMXBean/GetThreadAllocatedBytes/baseBehaviorTest_directly/TestDescription.java
vmTestbase/nsk/monitoring/ThreadMXBean/GetThreadAllocatedBytes/baseBehaviorTest_proxy_custom/TestDescription.java
vmTestbase/nsk/monitoring/ThreadMXBean/GetThreadAllocatedBytes/baseBehaviorTest_proxy_default/TestDescription.java
vmTestbase/nsk/monitoring/ThreadMXBean/GetThreadAllocatedBytes/baseBehaviorTest_server_custom/TestDescription.java
vmTestbase/nsk/monitoring/ThreadMXBean/GetThreadAllocatedBytes/baseBehaviorTest_server_default/TestDescription.java
vmTestbase/vm/mlvm/indy/func/jdi/breakpoint/Test.java
vmTestbase/vm/mlvm/indy/func/jdi/breakpointOtherStratum/Test.java
vmTestbase/vm/mlvm/indy/func/jvmti/stepBreakPopReturn/INDIFY_Test.java
vmTestbase/vm/mlvm/indy/stress/jdi/breakpointInCompiledCode/Test.java
vmTestbase/vm/mlvm/meth/func/jdi/breakpoint/Test.java
vmTestbase/vm/mlvm/meth/func/jdi/breakpointOtherStratum/Test.java

1.1 The tests failure appear in loom-repo, and most of these failures also reproduce in main-line repo, except the 4 tests run passed in main-line repo:
serviceability/jvmti/events/MonitorWaited/monitorwaited01/monitorwaited01.java
vmTestbase/nsk/jdi/ObjectReference/referringObjects/referringObjects003/referringObjects003.java
vmTestbase/vm/mlvm/indy/func/jvmti/stepBreakPopReturn/INDIFY_Test.java
vmTestbase/nsk/jdi/stress/serial/heapwalking001/TestDescription.java

1.2 These tests fails on linux-x64 with default VM option and with fastdebug jdk binary which build from loom-repo:
runtime/logging/VtablesTest.java
serviceability/jvmti/vthread/SuspendResume1/SuspendResume1.java#debug
serviceability/jvmti/vthread/SuspendResume2/SuspendResume2.java#debug

1.3 These tests fails on linux-x64 with -Xcomp VM option and with release jdk binary which build from loom-repo:
jdk/jfr/jvm/TestVirtualThreadExclusion.java
sun/security/ssl/SSLSessionImpl/ResumptionUpdateBoundValues.java
java/nio/charset/coders/StreamTimeout.java


2. These tests fails on linux-x64 with default VM option and with release jdk binary which build from main-line repo:
com/sun/management/ThreadMXBean/ThreadAllocatedMemory.java#G1
com/sun/management/ThreadMXBean/ThreadAllocatedMemory.java#Serial
com/sun/net/httpserver/bugs/B6431193.java
java/io/File/GetXSpace.java
java/io/FilePermission/MergeName.java
java/lang/management/ManagementFactory/ProxyTypeMapping.java
java/lang/management/ManagementFactory/ValidateOpenTypes.java
java/lang/management/ThreadMXBean/LockedMonitorInNative.java
java/lang/management/ThreadMXBean/ThreadCpuTime.java
java/lang/management/ThreadMXBean/ThreadUserTime.java
java/net/DatagramSocket/InterruptibleDatagramSocket.java
java/nio/channels/DatagramChannel/InterruptibleOrNot.java
java/nio/channels/SocketChannel/ShortWrite.java
java/security/AccessController/LimitedDoPrivileged.java
jdk/jfr/api/consumer/TestRecordedEventGetThread.java
jdk/jfr/api/consumer/TestRecordedObject.java
jdk/jfr/api/consumer/security/TestStreamingRemote.java
jdk/jfr/event/runtime/TestThreadStartEvent.java
jdk/jfr/jvm/TestGetAllEventClasses.java
runtime/cds/appcds/jigsaw/classpathtests/EmptyClassInBootClassPath.java
runtime/cds/appcds/jigsaw/modulepath/OptimizeModuleHandlingTest.java
serviceability/jvmti/events/NotifyFramePopStressTest/NotifyFramePopStressTest.java
sun/security/util/Resources/early/EarlyResources.java
tools/jimage/JImageToolTest.java
vmTestbase/nsk/sysdict/vm/stress/chain/chain007/chain007.java


3. several tests observed as inttermittent fails
3.1 compiler/jvmci/TestEnableJVMCIProduct.java intermittent fails on linux-x64 in loom-repo
3.2 runtime/Thread/ThreadCountLimit.java#id0 intermittent fails on linux-x64 with fastdebug build in main-line repo
3.3 jdk/jfr/event/gc/detailed/TestZPageAllocationEvent.java#ZGenerational intermittent timeout on linux-aarch64 in main-line repo, which maybe has been fixed by JDK-8278537 in loom-repo
3.4 java/lang/RuntimeTests/exec/LotsOfOutput.java intermittent fails on linux-aarch64 in main-line repo
3.5 java/lang/management/ThreadMXBean/ResetPeakThreadCount.java intermittent fails on linuxx64 with fastdebug build in main-line repo

4. Total 6 tests fails in jdk21u-dev repo
jdk/jfr/event/runtime/TestThreadDumpEvent.java (Maybe fixed by JDK-8334215 and JDK-8330846)
serviceability/jvmti/vthread/VThreadEventTest/VThreadEventTest.java (recorded by JDK-8322206)
sun/management/jmxremote/startstop/JMXStatusPerfCountersTest.java (Maybe fixed by JDK-8336257)
sun/management/jmxremote/startstop/JMXStartStopTest.java (Maybe fixed by JDK-8336257)
sun/management/jmxremote/startstop/JMXStatusTest.java (maybe fixed by JDK-8207908)
java/lang/management/ThreadMXBean/Locks.java (Maybe fixed by JDK-8306446)
4.1 com/sun/jdi/FinalizerTest.java intermittent fails in jdk21u-dev repo (Maybe be same to JDK-8343606)