When uploading files for printing without using the online editor, how much margin should I leave so that the file is not cut or leaves undesired margins?

Whenever you upload the files you must leave a safety margin so we can proceed with the cut.

In the case of decoration you should include 1 cm (5mm on each side) In the case of the canvas specifically 10cm (50mm on each side)

These dimensions are approximate to ensure that your final project will not be affected.