In the previous version of the OSG Seminar Manager, there were 5 pre-defined fields for courses. They could be used for texts. In this version, they are replaced by custom fields like the ones used for e.g. the booking form..
Due to this change, you can now use different types of fields for courses. Also, there is no limit for the number of custom fields you can use for courses any more.
If you update the OSG Seminar Manager from a Joomla! 3 version to the new Joomla! 4 version, the "old" custom course fields will be translated to the new custom fields.