Mariadb multi stage container with an existing database

I need to create a container with an existing database and operate some actions on it before distribute it. In production, I've got some really big databases:

[root]# ls /home/db-backup/test/prepare/26_06_2020/full/
ibdata1        
ib_logfile0    
ib_logfile1    
ibtmp1         
mysql
performance_schema
my_existing_database1
my_existing_database2
my_existing_database3

I just need to publish a container with my_existing_database1 for my team.

I tried many Dockerfile but I can't find a way do to it and I don't understand why. Here a simplified Dockerfile :

FROM mariadb:latest as builder

ENV MYSQL_ALLOW_EMPTY_PASSWORD yes

# for easier debug, i will remove that in prod
RUN sed -i '/\[mysqld\]/a plugin-load-add = auth_socket.so' /etc/mysql/my.cnf

WORKDIR /initialized-db

COPY ibdata1 .
COPY mysql ./mysql
COPY performance_schema ./performance_schema
COPY my_existing_database1 ./my_existing_database1
COPY db-init.sh /docker-entrypoint-initdb.d/

RUN chown mysql:mysql . \
  && chmod 660 ibdata1 \
  && chmod +x /docker-entrypoint-initdb.d/db-init.sh

RUN ["/usr/local/bin/docker-entrypoint.sh", "mysqld", "--datadir", "/initialized-db", "--aria-log-dir-path", "/initialized-db"]

# No file named test
RUN ls /initialized-db/

FROM mariadb:latest
COPY --from=builder /initialized-db /var/lib/mysql

As you can see, I try to execute my script db-init.sh. Simplified version :

#!/bin/bash
set -e -x

mysql -u root -e "CREATE USER 'test'@'%' IDENTIFIED BY 'test';"
touch /initialized-db/test

Unfortunetly, my script is not executed as the file test is not created. I try to bypass the /usr/local/bin/docker-entrypoint.sh with my own script (copy/paste of the file with some edit) but it's not working either (user and file test not created).

Can you help me on this one please?