Delete from a derived table in SQL Server?

I am studying the query in the answer of the post IN operator in SQL Statement Does not work?, as below:

DELETE t
    FROM (SELECT t.*,
                 ROW_NUMBER(*) OVER (PARTITION BY P ORDER BY ABS((P & 0xFFFFFFFF) * 256 - F) as seqnum
          FROM MyTable t
         ) t
     WHERE seqnum > 1;

After many researchs, I finally figure out most of the issues, and revised the query as below:

DELETE t2
    FROM (SELECT t.*,
                 ROW_NUMBER() OVER (PARTITION BY P ORDER BY ABS((P & 0xFFFFFFFF) * 256 - F)) as seqnum
          FROM MyTable t
         ) t2
     WHERE seqnum > 1;

The changes are:

1. Add ")" after "F)", so that "OVER (PARTITION BY P ORDER BY ABS((P & 0xFFFFFFFF) * 256 - F))" follow the syntax at https://docs.microsoft.com/en-us/sql/t-sql/queries/select-over-clause-transact-sql?view=sql-server-ver15
2. Change ROW_NUMBER(*) to ROW_NUMBER() since the document above use ROW_NUBMER().
3. Change the t in the outer query to t2. The subquery in FROM clause must have an alias, so there must be an alias after the subquery. See (T-SQL) Why does this subquery need an alias? . Moreover, actual the alias in the outer query can be same as the one in the subquery, see https://dba.stackexchange.com/questions/16516/subqueries-aliases-same-as-main-queries-aliases, but they are refer to different objects. So I change the alias in the outer query from "t" to "t2"

It is a bit difficult for a novice to understand many knowledges in a complex query. Whatmore, I still have two things that cannot understand very well.

1. Why I must write "Delete t2 FROM" instead of "Delete FROM"? I only find this link Difference between DELETE and DELETE FROM in SQL? , but it is used for JOIN table, not for subquery.
2. From the link at https://dba.stackexchange.com/questions/120233/sql-server-delete-from-subquery-derived-table, I know the subquery is a derived table. Then the DELETE from t2 is just delete records from a dervied table(it is virtual), why it can also perform the same deletion operation on the underlying real table MyTable?

Thanks

"Why I must write "Delete t2 FROM" instead of "Delete FROM"?

The easiest way is first to write a query that makes selection and then delete from it, for instance by using CTE:

WITH cte AS (
   SELECT * 
   FROM (
     SELECT t.*,
       ROW_NUMBER() OVER (PARTITION BY P ORDER BY ABS((P & 0xFFFFFFFF) * 256 - F)) as seqnum
     FROM MyTable t) sub
   WHERE seqnum > 1
)
SELECT * FROM cte; -- selecting
--DELETE FROM cte; -- deletion, no where condition, only the ones selected will be removed

Then the DELETE from t2 is just delete records from a dervied table(it is virtual), why it can also perform the same deletion operation on the underlying real table MyTable?

It is similar case to deleting from view. Rows can be deleted from derived table as long as SQL operations preserve key(no aggregations, DISTINCT, n:m relationship).

In this scenario adding window function introduces one new column, but it is always 1:1 to the existing data.