Disable Apple Intelligence for MacOS Mail

Turn email summary previews on or off

When you turn on Apple Intelligence, summaries automatically appear under your emails. You can turn off summaries and choose to see the first lines of the most recent message instead.

Go to the Mail app on your Mac.

Choose Mail > Settings, then click Viewing.

Select or deselect Summarize Message Previews.

Use Apple Intelligence in Mail on Mac - Apple Support

Refer to link below and specifically the section entitled

Turn email summary previews on or off

Use Apple Intelligence in Mail on Mac

You are welcome

Though, to be fair and balanced

I was the late comer to your question.