@joseph_1979
Thanks, but no such process appears on the task Manager.
Finally I erased the whole reolink folder and only then was I able to install the updated version of Reolink client.

I'm having a similar issue with this same version 8.12.1 on my Win10 PC. Update fails because "Reolink is still running". Even after a fresh reboot when using the installer file (as opposed to the updating option within reolink software which has te same failed result). However, I cannot find any process with the reolink name nor description.
Trying to uninstall 8.12.1 also fails with the same error (Reolink is still running).

Can you tell me what the process name is so I can kill it?

The only process that is running and called Reolink is the installer itself. Seems like the (un)installer is confusing its own task as the Reolink client.