Do client nodes help determine the master status

If I had a cluster with 2 data/master nodes and a 3rd client node, will the client node help avoid a split-brain if one of the other nodes in unavailable? I know this config is not recommended - I'm just trying to understand if they help determine master state.

By definition a client node is not master eligible, so it will not help avoid split-brain scenarios.

ok -thanks.

I'm trying to find the minimal set up for another node to avoid split-brain where there are really only two servers doing the heavy lifting. So if I make the 3rd node a master node, but not data, that would solve the problem?

If there a way to make the cluster prefer one of the data nodes as the master (eg, this 3rd server is really for other things and I don't want any extra work on it.)

If all 3 are master eligible, yes it will help maintain majority quorum.
You cannot set preference on which will be master though.