Hi Leo.
Before I try messing with wildcards, can I just ask this?
Is it not as simple as adjusting the column widths to how I want, then saving it for ALL music folders?
What do you mean by "all music folders"? How are you defining what a music folder is?
Directory Opus automatically decides that it is a music folder, hence the music columns.
Album, Artist, Year, Track, Duration.
That would be the Music format under Content Types, in the same Preferences page I mentioned. (Content Type detection is off by default, but must be on if that's being used automatically.)
Where do I find the content type detection settings?
I like how it does it though. I just wish I could get the columns to stick for all folders of a particular content type. I'll have a look at what you mentioned previously.
OK. I am getting somewhere now.
I changed the Music folder format filename column setting from blank to fill and it seems to have stopped the need to horizontal scroll. I tried Auto, and it didn't appear to do anything.
I might experiment with the Expand and Collapse settings.
The video at the bottom of Folder Formats: Quick Guide explains what auto/expand/collapse do in detail.
Thanks. I'll watch that.
By the why. I can't find those folder options explained in the help file as depicted in this video screenshot.
It sounded like you were already using them.
Thanks DesertDwarf.
I know that there is a Folder Options help section.
But the point I was trying to make is the current Folder Options page doesn't explain Auto, Expand, Collapse, Fill for column widths as pictured above. Unless I'm blind. 
They're explained on the Folder Options / Columns page:
https://www.gpsoft.com.au/help/opus12/index.html#!Documents/FolderOptions/Columns.htm
Ah, it's under "Folder Options Dialog". I never thought it would be under there.
I was blind, but now I can see. 
Where did your screenshot above come from? I was confused because it looked like you had posted a screenshot of what you were looking for. On closer inspection, it looks like it's from an older version of the manual, which wasn't clear to me.
You can always use the manual's search tab if you can't find something.
F1 in a dialog should also open the manual on the section about the dialog, in general.
It came from the video which I found at the bottom of the Folder Formats: Quick Guide that you posted above.
Ah, thanks. I thought it was your own screenshot, which confused me. The manual has changed in places since the video was made, but YouTube don't let you edit videos without breaking all the old links to them. 
No problem.
I've learnt a bit since I started this thread.
The columns not persisting were really annoying me.
I guess I must have enabled Folder Content Type Detection years ago.
I didn't know that it wasn't on by default. I wouldn't want it turned off though.
If it was turned off, would that mean I'd have the same columns for all folders? For example, music folder columns are completely different to data folder columns.
You can assign different formats to different paths (or path wildcards) whether Content Type Detection is on or off. If you want formats to be applied automatically based on folder contents then you'd need to keep Content Type Detection on, since that's the purpose of it, but it isn't the only way to view different folders with different columns.
That way sounds more cumbersome setting up multiple folders.