There is no option to configure external_ids:ovn-encap-tos in RHOSO, previous releases have this option available as Heat template parameter "OVNEncapTos" as part of https://review.opendev.org/q/topic:%22bug/1987382%22 .
As part of DT[1] this parameter is needed to be set

Option is not available in ovn-opertator and edpm-ansible ovn roles for this. It's needed to be checked where this config needs to be set and accordingly implement in ovn-operator and/or edpm-ansible roles.

For manual setup can do ovs-vsctl set open . external_ids:ovn-encap-tos="inherit" on the nodes where it's needed.

 [1] https://github.com/openstack-k8s-operators/architecture/blob/c8d33202dcfc5cec636ec64e49808ea106ea813a/examples/dt/neutron/3cont_2comp-ipv6-all-geneve-dvr-stf-rally