Bar chart : wrong values in x axis (mysql query gives the good ones)

I make it more simple, let’s take an “orders” table
The dashboard query is :

 select category, concat(year(order_date), '/', month(order_date)) as year_month, 
count(*) as tcount
    from orders
    where order_date >= '2023-11-01'
    group by category, year_month

So I would like to obtain 3 groups of tcount bars, x axis getting values “2023/11”, “2023/12” and “2024/01”, and one bar by category for each

First, Grafana tells me “Bar charts requires a string or time field” This 3 values are sring, so what ? So I go to the transform-date tab :
1/ I set year_month as Time
2/ I use partition-by-value, I add the field category

The resulting bar chart is good but the x axis vaues are 11/01, 12/01, 01/01, as if it was the first day of each month.