It looks like the addon is out of date, or had a dependency on another addon (possibly Chrome) which no longer includes those libraries.
Try installing this version of the addon - it's for LE9, so may not work with LE8.2.5:
I uninstalled the previous addon and installed your version, and the 2 dependencies are gone! and TigerVNC works as expected
LibreELEC:~/.kodi/addons/service.tigervnc/bin # ldd /storage/.kodi/addons/service.tigervnc/bin/x0vncserver
libX11.so.6 => /usr/lib/libX11.so.6 (0x00007f575b480000)
libXext.so.6 => /usr/lib/libXext.so.6 (0x00007f575b46e000)
libz.so.1 => /usr/lib/libz.so.1 (0x00007f575b458000)
libpthread.so.0 => /usr/lib/libpthread.so.0 (0x00007f575b437000)
libstdc++.so.6 => /usr/lib/libstdc++.so.6 (0x00007f575b2b4000)
libgcc_s.so.1 => /usr/lib/libgcc_s.so.1 (0x00007f575b29a000)
libc.so.6 => /usr/lib/libc.so.6 (0x00007f575b0e5000)
libdl.so.2 => /usr/lib/libdl.so.2 (0x00007f575b0e0000)
/lib64/ld-linux-x86-64.so.2 => /usr/lib64/ld-linux-x86-64.so.2 (0x00007f575b5ac000)
libm.so.6 => /usr/lib/libm.so.6 (0x00007f575af5f000)
Many thanks again for your help...