Can you show the contents of your .env file?
# egrep ^[^#] .env
DOMAIN=mmtest.mydomain.com
TZ=UTC
RESTART_POLICY=unless-stopped
POSTGRES_IMAGE_TAG=13-alpine
POSTGRES_DATA_PATH=./volumes/db/var/lib/postgresql/data
POSTGRES_USER=mmuser
POSTGRES_PASSWORD=mmuser_password
POSTGRES_DB=mattermost
NGINX_IMAGE_TAG=alpine
NGINX_CONFIG_PATH=./nginx/conf.d
NGINX_DHPARAMS_FILE=./nginx/dhparams4096.pem
CERT_PATH=./volumes/web/cert/cert.pem
KEY_PATH=./volumes/web/cert/key-no-password.pem
HTTPS_PORT=443
HTTP_PORT=80
MATTERMOST_CONFIG_PATH=./volumes/app/mattermost/config
MATTERMOST_DATA_PATH=./volumes/app/mattermost/data
MATTERMOST_LOGS_PATH=./volumes/app/mattermost/logs
MATTERMOST_PLUGINS_PATH=./volumes/app/mattermost/plugins
MATTERMOST_CLIENT_PLUGINS_PATH=./volumes/app/mattermost/client/plugins
MATTERMOST_BLEVE_INDEXES_PATH=./volumes/app/mattermost/bleve-indexes
MM_BLEVESETTINGS_INDEXDIR=/mattermost/bleve-indexes
MATTERMOST_IMAGE=mattermost-team-edition
MATTERMOST_IMAGE_TAG=7.1.2
MATTERMOST_CONTAINER_READONLY=false
APP_PORT=8065
MM_SQLSETTINGS_DRIVERNAME=postgres
MM_SQLSETTINGS_DATASOURCE=postgres://${POSTGRES_USER}:${POSTGRES_PASSWORD}@postgres:5432/${POSTGRES_DB}?sslmode=disable&connect_timeout=10
MM_SERVICESETTINGS_SITEURL=https://${DOMAIN}