How to disable "Organize by Conversation" in Apple Mail?

Re: "In Apple Mail, mail is stuck in Organize by Conversation even if turned off: No matter what, the setting in the View menu, Organize By Conversation -- even if I did not turn it on -- it's on"

Seems the View menu in the top menu of the Mail app just reflects what is set in Mail > Settings.

Am using an earlier MacOS version than yours, so there may be a slight variation, yet settings below may help:

You can Change settings to control how messages are shown in the Message viewer.

With Mail app open:

Click Mail (in the top menu bar) >

Choose "Settings (from the menu that opens) >

Choose "Viewing (from the window's top menu>

Under "View Conversations" untick every tick-box

If needed:

Apple Support's online article for MacOS Sequoia: Change settings in Mail on Mac - Apple Support

or

Mail Support webpage (info / support / contact options etc,): Mail - Official Apple Support

Thank you kindly for your thoughtful reply, Jeff, and for letting us know how you solved the issue you had! Cheers :-)