… The last time the question was asked 6 years ago in v25, and the answer doesn't make any sense when I try it follow it …

You are using Mac Finale v26 - right?

I do not know what the answer was 6 years ago.

But this solution works for me:

Use the Time Signature Tool.

Double-click the first measure, and set the 12/8 time signature as

Beats: 4

Beat Duration: Dotted Quarter

- which will give the 3+3+3+3 beaming as well as 4 slashes per measure.

Thanks for laying this out, Peter. And forgive the delayed response. The 6-y-o discussion was apparently sometihng far more arcane: https://makemusic.zendesk.com/hc/en-us/community/posts/360016096973-slash-notation-in-time-signature-for-display