Hi Kazuyoshi,
Excellent, thank you! That failure with runtime_cxxmodules=On is tracked here: https://sft.its.cern.ch/jira/browse/ROOT-10701 and was also reported at Issues building with v6.20.04 with GCC 10.1.1
Btw, your initial report on RLogger.hxx is fixed by https://github.com/root-project/root/pull/5775 Thanks for your report!
Cheers, Axel.