When enabling OneClick support from within Beat Saber Mod Manager, desktop files are created in ~/.local/share/applications/. The exec field pointing towards BSMM does not have correctly escaped spaces if they are present in the path. This can be easily resolved by wrapping the path string in quotes.

Example

Current:
Exec=/run/media/james/nvme0n1p1/App Images/BeatSaberModManager --install %u

Fixed:
Exec='/run/media/james/nvme0n1p1/App Images/BeatSaberModManager' --install %u

Furthermore, if attempting to fix this manually by editing the desktop file, the desktop file will be deleted and oneclick support marked as disabled the next time BSMM is launched.