Looks like that eLux doesn't install the folder /usr/lib/vmware/view/software, this is a folder packaged in Horizon Linux Client installer package, not sure why eLux doesn't integrated this folder

For /etc/vmware/config with rtav.codec="VmwTheoraSpeex", I think this will make RTAV works

Please double check the spelling and check if eLux forbid user to do any change to file system or not. After you adding this config, should relaunch the Horizon client and reconnect the view session to make it take effect. And after you reconnect the view session, double check if the setting still exists in /etc/vmware/config or not.

If it still failed, you can upload the log file /tmp/vmware-xxxx/vmware-RTAV-xxx.log with the latest one that after you adding this setting and launch view session to use RTAV.