Getting fade transition effect cycling through photos in "library" mode

When I am using the arrow keys to toggle between photos, the photos now fade in from black like a powerpoint slide. This is very annoying when I'm checking for differences between two photos. It wasn't doing that this morning so I assume I've hit a setting button somewhere, but closing and reopening did not help.

Lightroom Classic version: 12.1
License: Creative Cloud
Operating system: Windows 10 - Home Premium Edition
Version: 10.0.22621
Application architecture: x64
System architecture: x64
Logical processor count: 8
Processor speed: 1.9GHz
SqLite Version: 3.36.0