MySQL database fails to install when I try to create new custom site

When you run the first command, you have to wait until Docker actually creates the container:

docker container stop devkinsta_db && docker run --name devkinsta_reset_mariadb_root -v devkinsta_db_data:/var/lib/mysql/ -d mariadb:10.5.5 mysqld --skip-grant-tables

It can take a few seconds. If it successfully creates it, this command should return a basic log:
docker container logs devkinsta_reset_mariadb_root

Again, if you aren’t installing DevKinsta as the administrator, you’ll run into more issues.