Hi @julien 
,
In your collection B settings, you should see an option Allow record details display.
If checked, clicking on a record will display the record’s details page. If unchecked, a “Record access forbidden” message is shown. Note that if you hide a collection (from the left sidebar), this option will automatically be unchecked. You will have to manually check it to be able to access records from other collections (from relationship fields or related data).