Several years ago I created several custom auto layout presets for the Blurb book module of LrC. Over the years I have used them to make over a dozen books. A few months ago I bought an Apple M1 Mac, installed LrC, copied my catalog and templates to the Mac, and have been using LrC for months with no problems. But I had not used the book module since changing to the Mac. Currently LrC 11.5.
Today I decided I wanted to do some work on a new Blurb book, but now my custom auto layout presets do not appear in the book module. I verified that in the Lightroom/Lightroom Settings/Auto Layout Presets folder that my custom preset files (*.lrtemplate) are there.
I still have my Windows PC and all looks fine in LrC -- the templates are there in the book module. They are in the same folder as on the Mac.