您的配置基本上是正确的，但需要为kc.sh命令提供一个参数。如帮助输出所示，您的选项有：

build                   Creates a new and optimized server image.
start                   Start the server.
start-dev               Start the server in development mode.
export                  Export data from realms to a file or directory.
import                  Import data from a directory or a file.
show-config             Print out the current configuration.
tools                   Utilities for use and interaction with the server.

您可能需要start-dev，因此：

services:
  keycloak:
    image: quay.io/keycloak/keycloak:20.0
    command: start-dev
    .
    .
    .

使用KC_DB: mysql时我无法运行程序（这导致了Unknown database: MySQL错误），但使用MariaDB运行良好。

services:
  mysql:
    image: docker.io/mariadb:10
    environment:
      MARIADB_DATABASE: ${KEYCLOAK_DB_NAME}
      MARIADB_ROOT_PASSWORD: ${MARIADB_ROOT_PASSWORD}
      MARIADB_PASSWORD: ${KEYCLOAK_DB_PASSWORD}
      MARIADB_USER: ${KEYCLOAK_DB_USER}

  keycloak:
    image: quay.io/keycloak/keycloak:20.0
    environment:
      KC_HOSTNAME: localhost
      KC_HOSTNAME_PORT: 8080
      KC_HOSTNAME_STRICT_BACKCHANNEL: "true"
      KC_DB: mariadb
      KC_DB_URL: jdbc:mariadb://mysql:3306/${KEYCLOAK_DB_NAME}?characterEncoding=UTF-8
      KC_DB_USERNAME: ${KEYCLOAK_DB_USER}
      KC_DB_PASSWORD: ${KEYCLOAK_DB_PASSWORD}
      KEYCLOAK_ADMIN: admin
      KEYCLOAK_ADMIN_PASSWORD: ${KEYCLOAK_PASSWORD}
      KC_HEALTH_ENABLED: "true"
      KC_LOG_LEVEL: info
    healthcheck:
      test: [ "CMD", "curl", "-f", "http://localhost:8080/health/ready" ]
      interval: 15s
      timeout: 2s
      retries: 15
    command: start-dev
    ports:
      - 8080:8080

有了这个配置，我就可以访问http：//localhost：8080上的keycloak并登录到管理控制台。