After a bit of searching, it seems that this resolution is the same as the native resolution of Quest 1. I think they adjusted the display of the default magnification. I don't think I need to worry too much about it.

I'm having the same problem after yesterday's driver update. The maximum rendering resolution is fixed at 4128x2272 with x1.0. I don't know if this is what the developer intended or if it is a bug.