Adobe's Lightroom, known as Lightroom Classic to distinguish it from the cloud-based Lightroom CC, is one of the best image editing programs to be found. Undoubtedly, Lightroom Classic (Not Lightroom CC) is the best image management software by far with no rival to its combined functionality.
Despite this, there is no easy way to find all black and white images in Lightroom Classic, the closest method is to use Smart Collections.
Collections are one of Lightroom Classic's best ways to organise images, Smart Collections automatically find and add images based on criteria you set.
Here I'm going to create a Smart Collection for images that have been marked as Black and White in Lightroom Classic, so all of the images that I have converted to black and white using the program.
Here's how:
In the left hand side panel, scroll down to Collections
Click on the + to the right
In the context menu choose Create Smart Collection...