MariaDB 10.3

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WITH ranked_entity AS (
 SELECT
    table5.id,
    GREATEST(
        COALESCE(table1.dtEvaluationStart, '0000-00-00 00:00:00'), 
        COALESCE(table2.dtStart, '0000-00-00 00:00:00'), 
        COALESCE(table3.dtEvaluationStart, '0000-00-00 00:00:00'),
        COALESCE(table4.dtStart, '0000-00-00 00:00:00')) as dtStart,
    CASE GREATEST(
        COALESCE(table1.dtEvaluationStart, '0000-00-00 00:00:00'), 
        COALESCE(table2.dtStart, '0000-00-00 00:00:00'), 
        COALESCE(table3.dtEvaluationStart, '0000-00-00 00:00:00'),
        COALESCE(table4.dtStart, '0000-00-00 00:00:00')
        )
    WHEN COALESCE(table1.dtEvaluationStart, '0000-00-00 00:00:00') THEN 'table1'
    WHEN COALESCE(table2.dtStart, '0000-00-00 00:00:00') THEN 'table2'
    WHEN COALESCE(table3.dtEvaluationStart, '0000-00-00 00:00:00') THEN 'table3'
    WHEN COALESCE(table4.dtStart, '0000-00-00 00:00:00') THEN 'table4'
    END AS TableOrigin,
    ROW_NUMBER() OVER (PARTITION BY table5.id ORDER BY table4.dtStart DESC) AS rn
 FROM table5 
    LEFT JOIN table1 ON table5.id = table1.fid 
    LEFT JOIN table2 ON table5.id = table2.fid
    LEFT JOIN table3 ON table5.id = table3.fid 
    LEFT JOIN table4 ON table5.id = table4.fid
)
SELECT * FROM ranked_entity WHERE rn = 1;

id	dtStart	TableOrigin	rn
197	2020-11-18 10:14:31	table2	1
198	2020-03-01 09:40:09	table4	1