PostgreSQL SQL Error: Undefined function FROM_UNIXTIME

The solution is to use a use two different services. This is an example from core.

   entity.query.sql:
    class: Drupal\Core\Entity\Query\Sql\QueryFactory
    arguments: ['@database']
    tags:
      - { name: backend_overridable }
  pgsql.entity.query.sql:
    class: Drupal\Core\Entity\Query\Sql\pgsql\QueryFactory
    arguments: ['@database']

This should solve the problem for PostgreSQL and SQLite

$formula = $this->getDateFormat($this->format_string);

Drupal\views\Plugin\HandlerBase

/**
   * Creates cross-database SQL date formatting.
   *
   * @param string $format
   *   A format string for the result, like 'Y-m-d H:i:s'.
   *
   * @return string
   *   An appropriate SQL string for the DB type and field type.
   */
  public function getDateFormat($format) {
    return $this->query->getDateFormat($this->getDateField(), $format);
  }