Hi, this is a quickplay game. As with new formats like standard and expanded, it is still possible to play old formats in quickplay, which means you can just use any card you want but you wont get any progress for quests.
Thanks for the reply. I forgot I had attempted to join a quickplay game! Maybe I was to focused on being the first to join an open Gen 1 game and I didn’t bother to determine if it was quickplay or career because 95% of gen 1 games are in career mode.