SQL Server 2017

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DECLARE @T TABLE (ID INT, [Date] DATE, expected INT)
INSERT @T VALUES (117, '2023-11-14', 1),
                (117, '2024-01-25', 1),
                (117, '2024-02-01', 0),
                (117, '2024-02-04', 0),
                (117, '2024-02-11', 0),
                (117, '2024-03-04', 1),
                (118, '2024-01-02', 1),
                (118, '2024-01-28', 0),
                (118, '2024-02-04', 1),
                (118, '2024-02-18', 0),
                (118, '2024-03-11', 1),
                (118, '2024-06-05', 1)

;with cte as
(
  select id, date, expected, datediff(dd,lag(date) over(partition by id order by date), date) as datedif
  from @t
)

, cte2 as
(
select *
  , sum(datedif) over(partition by id order by date) as dd_sum
  , isnull(floor(sum(datedif) over(partition by id order by date) / 30.0),0) as counter
from cte
)

select id, date, expected
  , case when counter <> prior_counter then 1 else 0 end as flag
from (
  select *
      , isnull(lag(counter) over(partition by id order by date),-1) as prior_counter
  from cte2
  ) a

id	date	expected	flag
117	2023-11-14	1	1
117	2024-01-25	1	1
117	2024-02-01	0	0
117	2024-02-04	0	0
117	2024-02-11	0	0
117	2024-03-04	1	1
118	2024-01-02	1	1
118	2024-01-28	0	0
118	2024-02-04	1	1
118	2024-02-18	0	0
118	2024-03-11	1	1
118	2024-06-05	1	1

Warning: Null value is eliminated by an aggregate or other SET operation.