The plan viewer has different views:

• Heatmap: a table that lists all the processors and edges with relative metrics.

  The columns are sortable.

  Details are only available when running EXPLAIN ANALYZE (DISTSQL), rather than EXPLAIN (DISTSQL).

  Clicking on one or more IDs in the table will select them and assign a color; when switching to the graph view, the IDs (processors and links) are highlighted with the same color.

• Graph: A direct acyclic graph that shows how the various processors are used to execute the query.

  Hovering on the "Processor Name" will show additional details.

  Hovering on the links will show additional details, if available.

  Clicking on the "Node Name" will highlight all the processors running on the same node.

• SQL: The original SQL Query.
• Plan: The plan in JSON Format.

It uses the same encoding of the viewer at https://cockroachdb.github.io/distsqlplan/decode.html.
To use, simply modify the url generated by EXPLAIN ANALYZE (DISTSQL), replacing https://cockroachdb.github.io/distsqlplan/decode.html with https://cockroachdb.github.io/altdistsqlplan/decode.html.
Tested with CockroachDB v21 and later.