Unfreeze a frozen osx UI using ssh without shutting down all applications?

Unfreeze a frozen osx UI using ssh without shutting down all applications?

My mac freezes occasionally, and most often I simply restart it by holding
down the power button for 5+ seconds.
Today however, I had been running a huge file scan for 14 hours when the
UI froze completely, and I'd rather not wait another 14 hours!
Symptoms of the frozen UI: Nothing happens when using the keyboard (except
for the caps lock light turning on/off). Naturally, Force Quit does not
come up. Moving the mouse moves the cursor on the screen but clicking does
nothing.
Using another mac on the network, I can access the mac by ssh. I saw that
the RAM was almost full, but CPU activity was modest. Things I tried to
unfreeze the mac:
Shut down / kill Chrome, iMovie, Photoshop and other applications that I
didn't care about shutting down. Did help the RAM usage down, but did not
help in unfreezing the mac.
Shut down the Finder and Dock processes. No help.
Activated Screen Sharing from the command line and tried connecting
remotely. The password dialog comes up (indicating that screen sharing
indeed is activated) but after supplying password, the progress indicator
just spins for eternity and nothing happens.
Tried suspending the user session from the command line:
/System/Library/CoreServices/Menu\
Extras/User.menu/Contents/Resources/CGSession -suspend This command just
hangs in the ssh session and nothing happens. Needs to be aborted using
ctrl+c. Using sudo makes the command return immediately without any
effect.
Not even killing WindowServer (sudo killall -HUP WindowServer) helped, and
running a graceful restart (sudo shutdown -r now) only made the computer
freeze completely (no more cursor movements nor ssh access). Only the
power button force shut-off worked.
Had to wait another 14 hours for the file scan to run again :/ Is there
any other way to unfreeze a mac in this state? Would be good to know for
future reference…
Thankful for all tips!