Yes, with this minimal config, sound is playing. So I tried a little bit more adding and removing lines to and from the config and it turns out, that while this
server=192.168.1.33 sound=on
is working perfectly fine, the following
server=192.168.1.33 sound=on next screen application=chrome ...
Sorry, I was a little bit too fast with my answer. The client is not crashing anymore, but I have no sound at all. No matter if I choose hw:0:0 (HDMI) or hw:1:0 (and connect the 3.5mm audio jack), I do not hear anything.
I've just updated to WTWare 6.0.22 on my RPi4 (4GB). And now, when Windows (Win10 20H2) starts playing any sound, the WTWare RDP crashes (I get totally disconnected and end up on the Windows RDP login screen again).
I see this in the logs: [rdpclient 1219] [ 525.463165] Sound version: 8 ...
with Raspi 2b, 3b, 3b+ WTware was able to switch off (power off) the screen with hdmi_blanking=1 in the raspi config. This is not possible with Raspi 4. As stated here by the Raspberry Pi Foundation, this is a problem with the Raspberry Pi 4 itself, not WTware.
@aaronouthier I was one of the guys, who had sent a Pi 3b+ to wtware. But it took weeks to reach them. I just contacted them, and asked if I should send a Pi 4. But don't expect that to be quicker. It will again take weeks to reach them and then they can begin to work an a version supporting the Pi 4.