A simple solution is: in keycloak-main/js run frontend admin-ui by this command:
keycloak-main/js
pnpm --filter @keycloak/keycloak-admin-ui run dev
and for backend in keycloak-main/js/apps/keycloak-server run by this command:
keycloak-main/js/apps/keycloak-server
pnpm start --admin-dev