C:\ProgramData\Readarr
Unless otherwise specified Readarr will store it's application data in the home folder of the user Readarr is running under /home/$USER/.config/Readarr (~/.config/Readarr)
/var/lib/Readarr
/Users/$USER/.config/Readarr (~/.config/Readarr)
/usr/local/Readarr/var/.config/Readarr
/volume1/@appstore/Readarr/var/.config/Readarr
/share/MD0_DATA/homes/admin/.config/Readarr
/share/CACHEDEV1_DATA/Readarr_CONFIG
The -data= argument forces the location of the AppData folder, so your startup command may be forcing a specific location. This is required when trying to run multiple instances. On windows this would be /data=
The -nobrowser argument refrains from launching/opening the browser on startup. On windows this would be /nobrowser