Whisper-sync issue between Kindle and Audible on Mac after Sequoia 15.2 update

I've gone through several versions of instructions, but the steps seem to be outdated. One will say, go to Kindle settings and turn on Whisper-sync, but there's no choice for that under "settings." Another will say go to Amazon settings and make sure "sync" is turned on, and it IS turned on, but that doesn't fix my problem. All of the instructions I get seem to be out of sync with this current upgrade.

[Re-Titled by Moderator]