I have now tested the DVD folders on Kodi 20.0 for Windows. All can be played back without any problems.
serafis reported the same issue with CE 20.0_beta1: CoreELEC 20.0-Nexus_beta1 Discussion - #25 by roidy
And orlov at CE 20.0_rc1: CoreELEC 20.0-Nexus_rc1 Discussion - #5 by borygo