I don’t think it can be too large, but like others have said, there has to be enough quality content in each location you can visit to compensate for the vastness of the open world.

It be amazing if you could go inside every single building/dungeon/etc. and have every one of them chockablock full of things to experience, like they did with Elder Scrolls 6, but look how long it took for that game to come out…