GZDoom collects its IWAD candidates from [IWADSearch.Directories], reads
the support WAD there and the Load files from the IWAD's own folder
(src/d_iwad.cpp:456-476, 593-624, 862-901). RetroDECK lists
RETRODECKROMSDIR/doom there (gzdoom/rd_assets/rd_config/gzdoom.ini:9),
which component_prepare.sh:27 rewrites to $roms_path/doom. The extractor
read only the BIOS placeholder of a preset: it now records every line
naming the BIOS or the roms folder the script rewrites, with that sed
line in its source. $roms_path, whose default is the roms root
(config/retrodeck/retrodeck.json:5), is read as that root.
The profile names IWADSearch.Directories as a pool and lays its IWADs
and their support and Load files out at its top. On RetroDECK the 20
held IWADs land in roms/doom, the 23 others are named missing there.
The root copies stay for prboom and uzdoom, which claim them. No other
platform hands GZDoom that list, so none changes.