Virtual package vncviewer is provided by:
dpkg-query: no packages found matching xtightvncviewer Desired=Unknown/Install/Remove/Purge/Hold | Status=Not/Inst/Conf-files/Unpacked/halF-conf/Half-inst/trig-aWait/Trig-pend ||/ Name Version Architecture +++-===============-=============-==================================== ii tigervnc-viewer 1.12.0+dfsg-8 amd64 Virtual network computing client for X 1 packages