How to create an index when sql uses where and groupby?

When optimizing sql, due to the large amount of data, a simple sql but the execution speed is very slow
SELECT max( id ) FROM log WHERE create_date <= "2022-08-03" GROUP BY code

I have tried a variety of situations, create_date, code, (code, create_date), (create_date, code), using (code, create_date) to combine the index takes only 1 second at the fastest, using the explain command to view the two columns of the index useArrived, others need about 10 seconds

According to the information found on the Internet, a (create_date, code) index can be established. After all, where first and then groupby, but using explain, you can see that only create_date is actually used in the combined index
Why (code, create_date) is the mostQuick, what's the point of this