ACR fails to open

I have PS version 25.6 and ACR 16.2.1
Windows 10
When I try to open a raw file (nef), I briefly see a spinner in PS and then PS locks up. ACR never opens and I have to kill PS in Task Manager because I just get an audible alert with no dialogue or error messages displayed.
JPG and PSD files open like normal.
ACR filter does not work on JPG and PSD files, and it also locks up PS to where I have to kill again in Task Manager.