Ah, OK, I see what you mean.
The directory you're referring to is /storage/emulated/0/Android/data/com.thomasokken.plus42/files on my devices, and it can be accessed using the Files app, under Hamburger Menu → Device Name → Android → data → com.thomasokken.plus42 → files.
It would make sense if Plus42 stored its files there, where the Files app can access them, rather than in private storage, where the Files app cannot access them.
I'll look into changing that. It's a simple change in principle, but there could be some ramifications that I need to deal with.
For now, the only way to access the files is by copying them using Main Menu → File Import & Export.