This kind of problem is usually called gaps and islands, and there are quite a lot of examples here in stackoverflow, but i guess one more won't hurt:

;WITH CTE AS (
SELECT  TOP 1 WITH ties wonum, CONVERT(DATE, changedate , 103) AS date
,   changedate
, wostatus
FROM    (
    VALUES  (N'WO00001', N'21/3/2023 10:56', N'APPR', 100012)
    ,   (N'WO00001', N'21/3/2023 10:58', N'WAPPR', 100014)
    ,   (N'WO00002', N'22/3/2023 11:03', N'APPR', 100007)
    ,   (N'WO00002', N'24/3/2023 10:56', N'COMP', 100009)
    ,   (N'WO00003', N'21/3/2023 10:59', N'WAPPR', 100016)
    ,   (N'WO00003', N'21/3/2023 11:01', N'APPR', 100017)
    ,   (N'WO00003', N'24/3/2023 10:56', N'WSCH', 100018)
) t (wonum,changedate,wostatus,wostatusid)
ORDER BY row_number() OVER(partition BY wonum, CONVERT(date, changedate , 103)  ORDER BY CONVERT(datetime, changedate , 103) DESC)
)
, CTE2 AS (
    SELECT  *
    FROM    (
        VALUES(1),(2),(3),(4), (5), (6), (7),(8), (9), (10)
    ) v(c)
)
SELECT  a.*
FROM    (
    SELECT  *
    ,   DATEDIFF(DAY, LAG(date) OVER(PARTITION BY wonum ORDER BY date), date) AS prevDateDiff
    ,   LAG(wostatus) OVER(PARTITION BY wonum ORDER BY date) AS prevStatus
    ,   LEAD(wostatus) OVER(PARTITION BY wonum ORDER BY date) AS nextStatus
    FROM    cte
    ) dates
CROSS APPLY (
    SELECT  dates.wonum, dates.wostatus, dates.date, 0 AS calculatedFlag
    UNION ALL
    SELECT  dates.wonum, dates.prevStatus, DATEADD(DAY, -counter, dates.date), 1 AS calculatedFlag
    FROM    (
        select ROW_NUMBER() OVER( ORDER BY @@SPID) AS counter
        from CTE2 c
        cross apply CTE2 c2
        cross apply CTE2 c3
        ) c
    WHERE   c.counter < prevdatediff
    UNION ALL
    SELECT  dates.wonum, dates.wostatus, DATEADD(DAY, c.counter, dates.date), 2 AS calculatedFlag
    FROM    (
        select ROW_NUMBER() OVER( ORDER BY @@SPID) AS counter
        from CTE2 c
        cross apply CTE2 c2
        cross apply CTE2 c3
        ) c
    WHERE   c.counter < DATEDIFF(day, dates.date, GETDATE())
    AND nextStatus IS NULL -- Last workorder
    ) a

Here's one solution to the issue, it's a bit complex but i'll try to explain:

• First i want to get only the last date per worknumber and day. I use Top 1 with Ties and order by row_number to get only the last date

• Secondly, since we need to fill out dates, we want to have some sort of series. Usually your database might have a calender table that contains all dates, but maybe you don't, so i'm using a little apply thing that creates it.

• Third, we have 3 cases

• The actual worknum date

• Fill dates backwards from worknum dates

• Fill dates forward to today's date

• For each of the above cases, i create a separate UNION ALL inside the CROSS APPLY.

• First case is easiest, just take the data we have

• Second case, we want to use our series tables to generate a list of rows for every date that is different from previous dates.

• Third case is similar to second, but instead we fill up forward. Important to only fill up for the last workorder date, for that i use LEAD(wostatus) to make sure there are no more workorder dates in the future.

So yeah, it looks a bit involved, but maybe it's possible to understand, feel free to add questions and i'll try to explain a bit more in detail

EDIT:

To just use your table, change this part:

FROM    yourworktable t
/*(
    VALUES  (N'WO00001', N'21/3/2023 10:56', N'APPR', 100012)
    ,   (N'WO00001', N'21/3/2023 10:58', N'WAPPR', 100014)
    ,   (N'WO00002', N'22/3/2023 11:03', N'APPR', 100007)
    ,   (N'WO00002', N'24/3/2023 10:56', N'COMP', 100009)
    ,   (N'WO00003', N'21/3/2023 10:59', N'WAPPR', 100016)
    ,   (N'WO00003', N'21/3/2023 11:01', N'APPR', 100017)
    ,   (N'WO00003', N'24/3/2023 10:56', N'WSCH', 100018)
) t (wonum,changedate,wostatus,wostatusid)
*/