It has always done this to some extent, but as the other link I posted ([1]) describes, this both happens more frequently with the 3x lens on the 13 Pro than the 2x lens on previous generations because the 3x zoom has a smaller aperture than the 2x, and also the effect is more noticeable, because it's blowing a 1x image up to 3x rather than 2x.
I hope Apple will offer some facility to tweak this in future as it seems to me it frequently chooses digital zoom rather than the zoom lens even in "not that challenging" conditions. I do get why they'd do this though – the reality is that if it always used the zoom lens, you'd end up with a lot more noisy/blurred photos due to physics – but it would be nice to say "I'm OK with that"!
One other thing I should mention is that you can't set a third party camera app as the default, so the camera button on the lock screen always opens the stock camera. In practice I don't find this a huge issue, as if I'm grabbing a quick snapshot from the lock screen it might be of some fleeting moment, in which case I'd probably rather get a usable digitally zoomed image, than a blurry optical zoom one.
[1] https://lux.camera/iphone-13-pro-camera-app-intelligent-phot...
It's the auto-macro functionality in the camera settings. The default behavior switches to the ultra-wide below the minimum focus distance of the other two cameras.