VRF gateway can only be selected from the T0 which was used for the Supervisor enablement.
VRF Gateways under the T0 gateways other than the one used for Supervisor Enablement cannot be listed in the dropdown while creating a namespace and using the Override Workload Network Settings option.
vSphere with Tanzu 7.0
vSphere with Tanzu 8.0
This is expected behavior as per design on currently supported versions of Supervisors.
The VRF can only be selected from the T0 which was used for the Supervisor enablement.
This feature enhancement will be added in a future version.