Hi all.
Some Fedora users report this error (bugzilla ticket) by using xpra-2.3.1 (and with xpra-2.2.6 before):
$ xpra start :100 --start-child=xterm xpra initialization error: invalid mode 'start'
xpra is compiled with Python-3.6.5 with this configuration and available in the Fedora repositories if you can use it.
xpra does not fully support python3 yet (see #1568 and #853), you must use a python2 build to run the server for now.
You should not provide a build that cannot be used to run a server.
this ticket has been moved to: https://github.com/Xpra-org/xpra/issues/1885