As I said, I can't restore the "Files" application because when I reinstall it it no longer works. The other four applications mentioned are installed.
As I also said, the legacy mode scans folders (all) but does not find files inside.
It's strange but on my previous phone, Android 8, I didn't have this application either (I used MiXplorer as the only file browser) and yet Poweramp worked without problems, and without legacy mode.