With the recent release of OS X 11, we have been receiving reports that the ThinLinc client on this platform is launching as a blank window, and is therefore unusable. This appears to affect client versions 4.10.0 or newer, and is due removal of certain functions from the latest version of OS X.
We are currently investigating the issue, and have a bug open for it in our Bugzilla here:
Until an updated ThinLinc client is released, it is possible to use a nightly build as a temporary measure. The nightly build can be downloaded from the Cendio website here.