Fail to visulize the algo.unionFind result

To see a specific cluster in Browser, you probably want to specify the cluster ID in your query:

MATCH (n:HMGS)
WHERE n.cluster = 42
RETURN n

(although your screen cap shows the property as setId - whichever it is, you have to specify a specific community id).

You could also create a label for each community using apoc.create.addLabels and then manually specifying the color for each label in the browser UI:

MATCH (n:HMGS)
CALL apoc.create.addLabels( id(n), [ n.cluster ] )

That would let you see each of the communities with a different color when you queried the results.

Unfortunately, browser is a fairly simple visualization tool -- for large data sets, or anything more complicated, you would need to leverage something like Bloom or Linkurious.