JVMTI PopFrame() is returning OPAQUE_FRAME because virtual threads are not supported. A number of nsk/jdi and jdb tests fail because of this when using the virtual thread wrapper.

vmTestbase/nsk/jdb/pop_exception/pop_exception001/pop_exception001.java

vmTestbase/nsk/jdi/VirtualMachine/redefineClasses/redefineclasses002/TestDescription.java

vmTestbase/nsk/jdi/Scenarios/invokeMethod/popframes001/TestDescription.java

vmTestbase/nsk/jdi/BScenarios/hotswap/tc01x002/TestDescription.java
vmTestbase/nsk/jdi/BScenarios/hotswap/tc02x001/TestDescription.java
vmTestbase/nsk/jdi/BScenarios/hotswap/tc02x002/TestDescription.java
vmTestbase/nsk/jdi/BScenarios/hotswap/tc04x001/TestDescription.java
vmTestbase/nsk/jdi/BScenarios/hotswap/tc04x002/TestDescription.java
vmTestbase/nsk/jdi/BScenarios/hotswap/tc06x001/TestDescription.java
vmTestbase/nsk/jdi/BScenarios/hotswap/tc08x001/TestDescription.java
vmTestbase/nsk/jdi/BScenarios/hotswap/tc10x002/TestDescription.java

Note: vmTestbase/nsk/jdi/ThreadReference/popFrames/popframes001 was converted to support vthreads and expect the OPAQUE_FRAME error. The others were not because they don't add any additional value.

vmTestbase/nsk/jdi/ThreadReference/popFrames/popframes002/TestDescription.java
vmTestbase/nsk/jdi/ThreadReference/popFrames/popframes003/TestDescription.java
vmTestbase/nsk/jdi/ThreadReference/popFrames/popframes004/TestDescription.java