It seems like ZeniMax Online Studios (The Elder Scrolls Online) is currently about to start a new studio/office in San Diego. This was noticed by the Xbox insider Klobrille, who discovered the studio is currently hiring roughly 50 new people to the Hunt Valley and San Diego area to work on "the development of our next AAA game" which is also confirmed to be a "new IP," but is still only in pre-production.
ZeniMax Online Studios still hasn't confirmed that it has started a new office, but it would make sense as it is still working on new content for The Elder Scrolls Online and will continue to do so for years to come. This makes 50 new employees for a new IP seem like a brand new studio.
It's worth mentioning that ZeniMax (which of course includes ZeniMax Online Studios, but also companies like Bethesda and Id Software) currently is being bought by Microsoft. We don't know when this new game will be released, but you can be fairly sure it's going to be a part of Xbox Game Pass.