Is H5 supported in the Legacy (AKA Clarion) template chain?

No, H5 is not currently in the Legacy (AKA Clarion) template chain.

legacy is supported in the current versions (10,11), isn’t it?

It’s supported in Clarion 11 ‘Gold’ Build 13244

#TEMPLATE(Web, ‘Web Builder Templates H5-Bootstrap v11.0’),FAMILY(‘ABC’,‘CW20’)

Graham