You are trying to remove a failed/orphaned NSX manager node and delete option is greyed out in NSX UI
Cluster status shows degraded as in below screenshot because of the failed manager node.
Below is a screenshot from the UI wherein one of the manager nodes show no information and shows down.
VMware NSX
Failed NSX manager is still attached to the cluster when you run the below command.get cluster status
get cluster status
detach node faild_node_uuid
Note: When the detaching process is finished, run the command in step1 to view the cluster status again to see if the failed node was detached.If the failed manager node is still not removed from the UI even after detaching the node from the cluster, try running the below API call to delete the failed manager node.
DELETE https://<nsx-mgr-vip>/api/v1/cluster/nodes/<problem-NSX-manager-UUID>
Note: Please make sure you are entering the UUID of the problem manager.