Couldn't connect using the google credentials file. Provided the link with the following codes without using JSON.

const jwt = new google.auth.JWT(
      process.env.GOOGLE_SHEETS_CLIENT_EMAIL,
      null,
      process.env.GOOGLE_SHEETS_PRIVATE_KEY.replace(/\\n/g, '\n'),
      scopes
    );

    const sheets = google.sheets({ version: "v4", auth: jwt });

GOOGLE_SHEETS_PRIVATE_KEY

There is an important detail for the GOOGLE_SHEETS_PRIVATE_KEY environment variable. please add "\n" as character at start

"\n-----BEGIN PRIVATE KEY-----\nxxxxxxxxxxxx=\n-----END PRIVATE KEY-----\n"