Issues with uninstalling PulseAudio in order to get ScummVM sound

Raspberry Pi4 4GB
64-bit 20.04 Ubuntu Mate

I have previously put some posts up about this issue, but I think I have some more clarity now.

My Sound Preferences used to have two "Analog Out" entries under Output, one of which had "Headphones" noted in a bottom pane, and the other "HDMI". So I selected the HDMI option. Both outputs were Stereo.

In order to get ScummVM sound to work I tried uninstalling PulseAudio, as I am aware of ScummVM having issues around that on other builds. This does fix ScummVM sound, but also breaks YouTube sound (I can hear system sound effects).

Now, I get two BCM2835 options, both Mono. One is headphones, and one is HDMI. HDMI is now the default, and it is also set to Mute by default also. There is no longer any bottom pane, just a single section under "Outputs".

The sound is now muted when the Pi first boots up, and will mute again if I open Sound Preferences at any point. As mentioned, I no longer have sound coming through YouTube on my internet browser (Firefox). I used to be able to see which Applications were outputting sound on the "Applications" tab but that is always blank now.

Is there any way of having PulseAudio installed alongside ScummVM, or is this just the way it has to be for me?

It is a shame as I do like Ubuntu Mate, and I would like to stay; but I would like to have Internet Browser sound and Stereo sound so as it stands I would go back to Raspberry Pi OS once that has a more recent version of ScummVM available (they are currently on 2.0.0).