Hello Guiseppe, I am currently adopting the package and have a working unreleased version of tightvnc-jave available, which was built applying openjdk- 11.
As I don't possess any specific java knowledge I cannot judge whether this will fix the issue you reported. I will send you the deb file attached to a separate email and would like to ask you to test whether it fixes this bug for you. If it doesn't, I am afraid there is little what can be done, as upstream is dead. Regards, Sven
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