Maybe by ribbon and then title? Can you number the courses or put in something to make them in order by title? 
We put numbers in front of some of ours to kick them to the front of the line and I use ribbons to bring specific types to the top of the catalog (like Learning Paths). 

It would be great if we could choose the order without having to use numbers, but I haven’t found a good way either. 

Yeah we use course codes (a series of letters and numbers) to sort the courses in the order we want but are not a fan of having the course codes anymore. We are playing around with adding an enrollment date to on demand courses that don’t typically have a start or end date so we can try sorting by date.

We’ve made the group that we want to keep together start with the same word/case and found that works really well. I don’t have it anymore, but we got a list from support of the order of the sort. Maybe you can look to the sort order and come up with a creative way of wording the titles to keep them together. 

Grapevine response: Publishing date may work for you as well.

We are using the Access Date to sort items that we pull into featured content carousels. We set the access dates among the items that will be in the carousel so the dates are in the order we want the tiles to appear.  We pull the content dynamically using tags and then set the FCC widget sort order to Start Date. It's definitely a workaround solution, but it's been working out ok. 

We wanted to do the same thing, and we used publish date. When set manually you can sort by this date, if not filled in it will default to the actual publish date. So for us we boosted learning paths through a ribbon, then default order by most recently published and edited each publish date accordingly. 

Hi folks, this is not exactly what you all were asking about, but this suggestion might be helpful in your situation. Please check it out and upvote if you agree: 

Not only in the Catalog, but the way TI lists Titles in order confuses me. It would be nice if TI properly sorted Titles by Alphabetical/Grammatical Order. This is across the board for Catalog, Panoramas, etc.