You can apply for a traineeship at a company outside Belgium (even outside Europe) and gain your first work experience or do your trial period while being funded by Erasmus. For example, through an internship you can gain experience of a certain sector that may be outside your field of study. The maximum duration for a traineeship in a European country is 12 months, and for a non-European country 6 months.
After graduation, you will then officially become a “job seeker” and you will follow a corresponding course for job seekers. This permits you to go abroad with the status of “job seeker”. You cannot combine a traineeship with an employment contract. More information can be found at:
https://www.studentsonthemove.be/en/scholarships/erasmusplus-traineeship-after-graduation