relationships?

Could you please re-open this issue? I'm having the same issues on 2.01 and Drupal 10.

Is it possible to use a id's from a column in a remote table to create a relationship with a Drupal entity?

Just as an alternative for the solution above you can create database sql view instead and use it as a virtual table to display its fields in a Drupal view using the VDC module.

See how it could done for the mysql database driver: https://dev.mysql.com/doc/refman/8.0/en/create-view.html