My first question is what do you mean that you can't get it to run at all? What steps did you follow, and what results were you expecting to see (other than the programme running!)?**
Which version of OLP have you downloaded and tried to run?**
I understand that you haven't had any success, but there are two versions available to download. It would help me to know which one. I don't have a MacBook Air, but I have a 2012 Mac Mini and the latest version of macOS it can run is Catalina, so I'll be on the same path as you.
My next question for you is how much RAM do you have on the MacBook Air? And finally, what size is the main storage, and how much free space is there?
Has anyone else made the switch? you ask. Ha! My church is trying to force me to switch away from OLP to ProPresenter! I keep fighting them off, bravely or otherwise. As a result, we have had no projection at church since March this year because no one else has the expertise to do projection. Yet all of the heirarchy has the expertise to tell me what tools I need and what a bad job i'm doing with the tools I choose to use. (Sorry for that little outburst.)
So, if you can at least answer the first couple of questions I posed, that will help me to help you. I've marked those questions with **.