accidentally deleted all photos on Lightroom

check your "Deleted" folder immediately; Adobe usually retains files and their non-destructive edit metadata for 60 days before permanent purging. If they were deleted from Lightroom Classic and the disk, your best technical bet is a local system backup (Time Machine/Windows Backup) to restore the .lrcat catalog file, which contains all your edit history. Log in to the Lightroom web portal as well, as sometimes the sync latency leaves a "ghost" copy of the assets in the cloud even after a local deletion.

Unfortunately, recovery does not appear to be possible. 

Each device has a “Deleted Items” folder that allows for a 30 day recovery window - unless you also accidentally deleted them from that folder.