GDPR compliance

Answer:

If the processing is undertaken by an employee of an EU-established company and it is done only exceptionally for example when the employee is on a business trip then we are not in front of a cross border data transfer.

What if it is not exceptionally , but rather that the employee lives outside EU and "works from home" ?

In this case, the employer should ensure that any data on the device cannot be stored or processed locally.

One solution would be using a "remote desktop" solution such as Citrix. In this case, we would not be facing a data transfer.