You could use the query for each database.
SELECT
[name]
,create_date
,modify_date
FROM
sys.tables
or perhaps define modified time frame,
SELECT
[name]
,create_date
,modify_date
FROM
sys.tables
WHERE
modify_date > DATEADD(day,-30,GETDATE())
And take the Backup of the DB which have modified date between expected range.
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