SQL Server 2019

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CREATE TABLE raw_events (
    "owner_id"      INTEGER     NOT NULL,
    "event_id"      INTEGER     NOT NULL,
    "start_date"    DATE        NOT NULL,
    "end_date"      DATE        NOT NULL,
    PRIMARY KEY("owner_id", "event_id")
);
CREATE TABLE clean_events (
    "owner_id"      INTEGER     NOT NULL,
    "event_id"      INTEGER     NOT NULL,
    "start_date"    DATE        NOT NULL,
    "end_date"      DATE        NOT NULL,
    PRIMARY KEY("owner_id", "event_id")
);
INSERT INTO raw_events VALUES
(1004,3001,'2021-06-11','2021-06-19'),
(1004,3002,'2021-06-11','2021-06-19')
;

with cte as (
select 
    re.owner_id
    ,re.event_id
    ,re.start_date
    ,case when dateadd(day,-1, lead(start_date,1) over (partition by owner_id order by start_date)) < end_date
        then dateadd(day,-1, lead(start_date,1) over (partition by owner_id order by start_date))
        else end_date
        end as end_date --if overlaps or abuts then end on the day before the next event
from dbo.raw_events re
--omit events which are fully contained in another event including if it starts and ends on the same day
where not exists (select 1 from dbo.raw_events r2 where re.owner_id = r2.owner_id and re.start_date >= r2.start_date and re.end_date <= r2.end_date and re.event_id != r2.event_id ) 
)
select owner_id
        ,event_id
        ,start_date
        ,end_date
from cte
where start_date <= end_date --event cannot end before it starts
order by owner_id, start_date;

owner_id	event_id	start_date	end_date

/*
owner - think a person
event - an activity.  One owner can only be on one event at a time
        ten owners can be on ten different events at a time

Incoming data needs to fit the constraint - an owner can only be on one event on a given date.
In the full case there are tens of thousands of owners, millions of events, owners are independent of one another.
At present, events for an owner may overlap, abut and one may be completely contained within another.
Where one owner's shorter event is completely within a longer one, the shorter event should not be in the output.
When two events for an owner abut (one ends the same day another begins) the earlier event should 'end' one day earlier.
When two events for an owner overlap, the earlier event should be cut shorter until they neither overlap nor abut.
Events can start and end on the same date, but one event cannot end before it begins.
If two events for an owner have the same start and end date, return the one with the higher event_id.

Populate clean_events from raw_events satisfying the above requirements.
You may create intermediate tables if you need to.
Common table expressions, subqueries, window functions etc. are fine, but avoid user defined functions.
*/
SELECT
    owner_id,
    event_id,
    start_date,
    end_date
FROM raw_events
ORDER BY 1
;

owner_id	event_id	start_date	end_date
1004	3001	2021-06-11	2021-06-19
1004	3002	2021-06-11	2021-06-19