I’ve followed the instructions here: Quick Start to Keep SpamSieve Working With Apple Mail When Updating to macOS 14 Sonoma
and I’ve also followed the instructions under [4.5.4 Setting the Junk Mailbox in Apple Mail] here: SpamSieve Manual: Setting the Junk Mailbox in Apple Mail
BTW, since I’ve turned off Apple Mail’s “Enable junk mail filtering,” my Junk inbox is now flooded with junk emails received through iCloud that it used to filter out. It’s all bad.