I wasn't aware of the hardcoded /usr/local/lib path as everything is running from $HOME/xen-orchestra and node_modules directory full of symlinks was there too. It works now - thanks!
Testing xcp-ng 8.0 on two servers with ha-lizard-noSAN, so far so good. Now, where to find more settings of openvswitch? For the redundant replication link (DRBD/iSCSI) between two machines without a switch, I'd like to set up a bridge with (R)STP between one 1Gb and one 10Gb interface, where 1Gb is a backup if 10Gb link fails. The ha-lizard reference design calls for bonding two 1Gb interfaces with LACP and this was easy to set up in XenCenter, but bonding requires interfaces of the same speed.