I recommend the following definitions for the purpose of this topic:
host b: The computer on which you run the web browser to access the CryoSPARC UI.
host c: The computer on which cryosparc_master/ software was installed and is running.
userc: Is a Linux user that has ssh access on host c
ipaddrc: The IP address of host c.
If host b and host c are the same computer, port forwarding is not needed; you can access the CryoSPARC UI by pointing your browser to http://localhost:39000.
If host b and host c are different, you would run, on host b
ssh -L 62222:localhost:39000 userc@ipaddrc
and point your browser to http://localhost:62222. This example ssh command deliberately forwards a port with a different number from the UI port on host c, to avoid confusion and conflicts.
You will not be able to access the UI using either method if app is not running, as it is not in Problem with Cryosparc - #13 by shashi.