Working locally after cloning Craft 3 from Hyperlane
Solved. The config/db.php cloned from Hyperlane refers to different env variable names than those used within my .env file. Changing the names in config/db.php solved the issue.

Before:

return [
    'driver' =&gt; getenv('DB_DRIVER'),
    'server' =&gt; getenv('DB_HOST'),
    'user' =&gt; getenv('DB_USER'),
    'password' =&gt; getenv('DB_PASSWORD'),
    'database' =&gt; getenv('DB_NAME'),
    'schema' =&gt; getenv('DB_SCHEMA'),
    'tablePrefix' =&gt; getenv('DB_TABLE_PREFIX'),
    'port' =&gt; getenv('DB_PORT')
];


After:

return [
    'driver' =&gt; getenv('DB_DRIVER'),
    'server' =&gt; getenv('DB_SERVER'), // changed
    'user' =&gt; getenv('DB_USER'),
    'password' =&gt; getenv('DB_PASSWORD'),
    'database' =&gt; getenv('DB_DATABASE'), // changed
    'schema' =&gt; getenv('DB_SCHEMA'),
    'tablePrefix' =&gt; getenv('DB_TABLE_PREFIX'),
    'port' =&gt; getenv('DB_PORT')
];