When rebuilding my plugins for R2024, I had to notarize the Mac version again for the new builds. The process worked fine, but I noticed that there was a message from Apple stating that the use of 'altool' to notarize was not going to be supported by the end of 2023.
In fact, they now say "The Apple notary service no longer supports altool from November 1, 2023. You use notarytool instead." See https://developer.apple.com/documentation/security/notarizing_macos_software_before_distribution
So I looked into using 'notarytool' and surprisingly (for Apple and XCode) it's significantly simpler and faster than the previous method. I've written some notes on how to use it for anyone interested, which are on my site at https://microbion.co.uk/html/r2024macosnotarize.htm