Anytime that you copy data from a related table, that copy will not automatically update should you modify the original. If, however, you establish a link to a record in a related table, you can then place a field from the related table in your portal row and now your data will update.
But this will set up a one to one or many to one relationship, not the one to many relationship that you have described.
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As always, thank you for your quick response!
Well, I have linked those tables as described. But when I plase a field of the related table in the portal row (join table), then I can not add or select content in that field in the portal row. It is locked. Why that?
Perhaps because no record from that table is yet linked to the join table record? And maybe "allow creation of records via this relationship" is not enabled for the table into which you are trying to enter data?
Sometimes, you need buttons and scripts to better manage what you need to do when adding records and also linking them in to a join table.