Docker image is yet to be released on Docker Hub
In order to start container, execute command: docker-compose up -d or use plain docker command with proper parameters included in docker-compose.yml file.
Feel free to rewrite app-start.sh file to your needs, this file is used docker-compose to execute commands on container start. By default XAMPP start with only Apache loaded.
REMEMBER TO CHANGE PASSWORD OF USER IF YOU WANT TO USE FTP. This is quite simple, just get into shell of cointainer and execute this command: passwd xampp-user.
XAMPP version used in this project is: 8.1.4