Duckstation correctly supports the frontends.
am start -n com.github.stenzek.duckstation/.EmulationActivity -e bootPath "uri file"
The Launchbox teams is stubborn in not wanting to implement scoped storage correctly. Are you waiting for Duckstation or Google to put back the old file management without scoped? It seems a bit pretentious to me.
So if you don't have a phone older than 4 years with Android 10 or lower you can't use Duckstation and half of the other emulators. I understand that it takes time and creates problems to implement scoped storage, but now everyone has adapted, months and months have passed.
I paid $40 for an app that half works with thousand bugs and I don't use it anymore. Frontends like Daijisho are free, often open source and compatible with almost all emulators, including Duckstation which works perfectly. Such a price seems a bit like a scam to me considering the level and slow development of this app.