Festival Collection was a CFV convention set that was slated to be released before said convention was cancelled. Instead will have a booster box release in August 7th.
https://cf-vanguard.com/cardlist/cardsearch/?expansion=180
The full list of cards have been revealed on the Japan's site which reprints highly sought after and played cards in the CFV Standard such as every Draw Trigger Sentinels from all 24 Clans of Vanguard.
The set will also include an errata on all Starting Vanguard that adds the new quick shield mechanic introduced with the TRY3 Trial decks releasing in June 26th