Thanks @wilsj for your kind response and thoughts. I do of course understand the commercial bindings your are in and my P.S: about making the whole ThinLinc technology (incl. server) open source was of course meant to be the optimal case from my personal point of view only 
as there are IMHO tons of success stories out there where companies still produce revenue and can pay their employees thought their product is fully open source But I also understand your reservations of course.
However, coming back to the ThinLinc client, I still feel that this could be a complete different story here. While of course the server components are a bit more critical and perhaps way to much work to release them under open source, I still think that especially having the client released as open source could open up completely new ways of attracting certain new customers or interested parties. Just imaging the client and its build environment would have been open source right from the beginning. Others would have probably already done the job in creating an ARM64/aarch64 version of the client or even integrating the client technology into other general remote connection clients like "remmina” or similar., which would have provided you and the great ThinLinc technology way more visibility. And besides, it would have helped certain customers (like us) to create an own command-line client only which could then be directly integrated in a ThinClient environment like thinRoot, which we are developing and using ourself. And it would probably also helped to better fix certain still existing bugs and shortcomings in the client ourself instead of just being able to open bug reports and simply reverting to a previous client version in case some problems appear (e.g. like we have had when we moved to the 4.19.0 client recently - see https://bugzilla.cendio.com/show_bug.cgi?id=8686 or https://community.thinlinc.com/t/thinlinc-client-4-19-0-and-fullscreen-multi-monitor-session-re-connect-issue/1742 )
And while I can understand that the server components might still be better kept closed source from a commercial POV, I still feel that especially opening the client could in return provide you even more potential customers, visibility and benefirts if it would be open source while at the same time not threatening your main IP, which mostly is probably located in the server components…