create table tbA ( id int, jsonData varchar(max) )

insert tbA values (1,'{"updated_at":1664296267649490}') ,(2,'{"updated_at":1632984531588160}')

select id,DATEADD(SECOND, (cast(JSON_VALUE(jsonData,'$.updated_at') as bigint) / 1000000), '1970-01-01 00:00:00') as dateConverted from tbA