Bonjour Murat, You are correct that there are certain phrases that follow «que» where there is an accord with the subject in the main clause; it is named the CASE of the subordinate clause with que and the lesson follows: Special cases when the past participle agrees (in number & gender) when used with 'avoir' in the compound past in French (Le Passé Composé) There seems to be very specific cases where this is applicable. J'espère que cela vous aiderait. Ron (un locuteur non-natif)

Here is the rule: when the object of a sentence comes before the participe passé, the participe is matched to the object. Let's look at the example you cite: Je mange une pizza, que j'achetée en Italie. Here, "que" is the stand-in for pizza. It also precedes the participe "achetée". Hence achetée needs to be in the same number (singular, since only one pizza) and gender (feminine, since it is "la pizza"). Another example: Les bonbons que j'ai goutés avaient bons. Here "que" stands for "les bonbons", which are masculin plural. Hence "goutés" needs to match that. -- Chris (not a native speaker).