Settings > Import > Auto Import gains Include subfolders (off by default:
the watched folder's top level only, as before). On, the scan also lists
its subfolders' photos: hidden entries, links to folders and the library's
own folder (where copy-mode arrivals go) are skipped; at most 16 levels and
200,000 entries, with a warning when a bound is hit. An unreadable
subfolder or a non-Unicode name is skipped with a warning.
library.autoImport takes subfolders; library.autoImportScan reports it and
listingWarnings.