Well ... I cleared Chrome's cache and then restarted my Mac. This restarted Chrome and calibre. The
BrotliDecompress failed issue remains. Here is an url from FFN to test.
https://www.fanfiction.net/s/14450665/1/Brick-by-Brick
Chrome is Version 140.0.7339.81 (Official Build) (arm64), OSX is version 15.6.1 and the plugin is v4.48.1
FWIW, AO3 still works.
I also tried calibre in debug mode. I've attached the debug log file.
Stephen