The server encoding preference can now be customized with
QT_VNCSERVER_PREFERRED_ENCODING environment variable. Set this
to a semi-colon-separated list of encodings. The first that is
supported by the client will be picked. If none are supported
by the client, the client's first supported preference will be
chosen instead.

E.g.: QT_VNCSERVER_PREFERRED_ENCODING=hextile;zlib

This would make the server prefer hextile over zlib, even if the
client prefers zlib.