Wanted to report back after moving on to Ventura 13.2.1 - no more hard hangs and lockups with SMB. So I made the move back to SMB from AFP.
That said, I noticed what appeared to be corruption when using the built-in Preview.app on some pretty basic JPGs.
I copied the folder over to a local drive and it was fine via the Preview.app so I looked at the checksums:
[vger:/Volumes/data/corruption] emura% md5 -r * | sort | md5
430dc9f736edea0c6c0bdd433c04c5de
[vger:~/Desktop/corruption] emura% md5 -r * | sort | md5
430dc9f736edea0c6c0bdd433c04c5de
So things are fine at the slightly lower level, not going through Preview.app. I started to think there was a problem with mmap() or similar access via SMB, so I reproduced the Preview.app corruption and saw a ton of these:
10:35:41.505647 getxattr [ 93] /Volumes/data/corruption/FFF_7985_5f90a41a96b6c4c542e1992f81b4ce2b.jpg 0.000618 Preview.620542
10:35:41.542491 getxattr [ 93] /Volumes/data/corruption/FFF_8014_4e995cefb220d9a316d72c486dbcb87b.jpg 0.000499 Preview.620542
10:35:44.100537 getxattr [ 93] /Volumes/data/corruption/ABE_8232_8384c12d276c9156a1077d7d294aad37.jpg 0.000567 Preview.620602
10:35:44.108273 getxattr [ 93] /Volumes/data/corruption/ABE_8287_554421b278c1a7cba401aee06de4f339.jpg 0.000722 Preview.620602
This is "[Errno 93] Protocol not supported" - which correlates perfectly with the files and the symptoms, but not sure about the root cause, esp. since unsupported EA operations are generally not fatal nor important. Also, hitting the error right at open() so that the Preview.app throws the "cannot understand file xxx" is borderline okay, esp. in terms of observability and non-silent errors/corruption, but seeing other files in Preview.app displayed partially fine and then corruption further down the image - that's very, very disturbing.
Unmount and remount of the SMB share "fixed" things, but it's still unsettling to see this sort of behavior.