Here is the number of fields that can be displayed based on the view type:
Form: up to 6 fields if the view is List (depending on the Form Width). Other Layout Type available for form's linked records are - Grid and Gallery.
List view: up to 6 fields (depending on the Form Width)
Gallery view: up to 50 fields by setting in Custom preview fields (Select custom fields should be selected in Preview fields);
By default up to 3 fields will be displayed as preview fields (Use the same fields from the expanding form is selected in Preview fields).
Grid view: up to 49 fields
Kanban view: up to 6 fields by setting in Custom preview fields (Select custom fields should be selected in Preview fields); By default only the record title and the single select field set are displayed (Use the same fields from the expanding form is selected in Preview fields)