Repeat lines in Array: is it possible with UNNEST? or is there any other way? - Bigquery

Question

I made this query in SQL in Bigquery (Google):

SELECT
    FORMAT_DATE("%E4Y-%m", date) AS Mes,
    cliente,
    ARRAY_AGG( DISTINCT date ORDER BY date DESC LIMIT 2) AS date
FROM `iconic-rampart-279113.ranktank.IA_InternAll`
    GROUP BY Mes, cliente
    ORDER BY Mes, cliente ASC

It provides the last two dates of a month, that some customer has data, but would like to know how to fill in the blank values of the image.

enter image Description here

Researching I found some queries with UNNEST but I did not understand, let alone know how to reproduce.

Or is there any other way to bring the data? (Month, client, date)