I'm having a hard time loading the theme. If I set it as the "displays menu" theme I get a large message saying "don't use arcade flow as the displays menu layout". When I set it as my theme for NES, I get a large arcadeflow logo with a gray loading screen type of screen. If I press "L" to get into the layout options menu, all I get is the layout file name tab.
First you don't have to set Arcadeflow as "display menu" layout, at least that's not recommended. AF already has its display menu UI so you can use that without setting it as display menu.
The other issue seems related to the version of AM+ you are using, is it the latest build from github? You can get it from here:
https://github.com/oomek/attractplus/actions/runs/4054858529scroll to the bottom of the screen and you'll be able to download binaries (you need to be logged with a github account).
If you still have issues, I'll need a log or the console output to debug.