First spotted by a user on Reddit, a number of EA Maxis vacancies revealed the studio was ramping up a 'new, unannounced title', which it referred to as its 'next big production', asking for people specifically experienced in creating 'excellent user experiences for new IP'. It's also worth mentioning that back in January 2020, Maxis went on a huge hiring spree.
Interestingly, Maxis has started dabbling with some kind of timed Sims experiences in The Sims 4, with events like The Sims Sessions, which was a bit of a strange music festival that lacked the spectacle of other in-game events.