Xdebug is indeed enabled, but is set to xdebug.mode=off. This practically disables Xdebug with zero overhead, so this message should be silenced.
@@ -40,6 +40,7 @@ services:
image: markoshust/magento-php:7.4-fpm-11
volumes: *appvolumes
extra_hosts: *appextrahosts
+ env_file: env/phpfpm.env
db:
image: mariadb:10.4
@@ -0,0 +1 @@
+COMPOSER_DISABLE_XDEBUG_WARN=1