Transform buttons (i.e. auto, vertical, guided etc) not working in LR CC 15.6 after upgrading to Mac OS 27.0.1 (Golden Gate). Sliders still work though.

I just tested this on my 14” MacBook Pro M1 2021 with Mac OS 27.0.1, Lightroom 15.6, using several .NEF files from different older and newer cameras.
I used both Auto and vertical guided, and Transform worked like I am used to. I could not see any misbehavior. 
Could the problem be the catalog file? Is it optimized?

Lightroom and other Adobe products do not support new versions of macOS immediately upon their release.
It is possible that they may not function properly for about six months after a new OS version is released.