MariaDB / MySQL: Partial "total" number of rows for moving time-window - count

Question

I have a MariaDB Database with Users and their appropriate registration date, something like:
+----+----------+----------------------+
| ID | Username | RegistrationDatetime |
+----+----------+----------------------+
| 1 | A | 2022-01-03 12:00:00 |
| 2 | B | 2022-01-03 14:00:00 |
| 3 | C | 2022-01-04 23:00:00 |
| 4 | D | 2022-01-04 14:00:00 |
| 5 | E | 2022-01-05 14:00:00 |
+----+----------+----------------------+
I want to know the total number of users in the system at the end of every date with just one query - is that possible?
So the result should be something like:
+------------+-------+
| Date | Count |
+------------+-------+
| 2022-01-03 | 2 |
| 2022-01-04 | 4 |
| 2022-01-05 | 5 |
+------------+-------+
Yes it's easy with single queries and looping over the dates using PHP, but how to do it with just one query?
EDIT
Thanks for all the replies, yes, users could get cancelled / deleted, i.e. going by the max(ID) for a specific time period is NOT possible. There could be gaps in the column ID

Answer 1

Use COUNT() window function:
SELECT DISTINCT
DATE(RegistrationDatetime) AS Date,
COUNT(*) OVER (ORDER BY DATE(RegistrationDatetime)) AS Count
FROM tablename;
See the demo.

Answer 2

SELECT
date(RegistrationDatetime ),
sum(count(*)) over (order by date(RegistrationDatetime ))
FROM
mytable
GROUP BY
date(RegistrationDatetime );
output:
date(RegistrationDatetime )
sum(count(*)) over (order by date(RegistrationDatetime ))
2022-01-03
2
2022-01-04
4
2022-01-05
5
see: DBFIDDLE

Answer 3

SELECT t1.RegistrationDatetime AS Date,
(SELECT COUNT(*) FROM users t2 WHERE t2.RegistrationDatetime <= t1.RegistrationDatetime) AS Count
FROM users t1
GROUP BY t1.RegistrationDatetime

Answer 4

If you have no cancelled users, you can do:
SELECT DATE(RegistrationDatetime) AS date_, MAX(Id) AS cnt
FROM tab
GROUP BY DATE(RegistrationDatetime)
Check the demo here.
Otherwise you may need to use a ROW_NUMBER to generate that ranking:
WITH cte AS (
SELECT *, ROW_NUMBER() OVER(ORDER BY RegistrationDatetime) AS rn
FROM tab
)
SELECT DATE(RegistrationDatetime) AS date_, MAX(rn) AS cnt
FROM cte
GROUP BY DATE(RegistrationDatetime)
Check the demo here.