
For a container with phpMyAdmin, you need to add a variable with an absolute path:
PMA_ABSOLUTE_URI: "https://artem.services/phpmyadmin"
The "location" block for Nginx (change the proxy path to yours):
    location  ~ \/phpmyadmin {
        rewrite ^/phpmyadmin(/.*)$ $1 break;
        proxy_set_header X-Real-IP  $remote_addr;
        proxy_set_header X-Forwarded-For $remote_addr;
        proxy_set_header Host $host;
        proxy_pass http://localhost:8080;
    }
Now phpMyAdmin will be available along the path:
https://artem.services/phpmyadmin/