This isn't actually a bug, just a highly questionable design decision. To the left of the button which puts the screenshare in fullscreen and the button which pops the screenshare into a window is a volume button which controls the master volume of the entire VC. That it exists at all makes little sense to me, considering it is a completely redundant control that duplicates all the functionality of the volume button in the middle control set. The easiest solution is probably to just remove the redundant button.
I think it would be better to control the stream volume instead of removing
I just found that I could actually control the stream volume because I randomly did right click
which is the same behaviour as discord
Edit:
#3157 humpus fixed it! Thanks
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Comment by @dicamarques14
which is the same behaviour as discordEdit: #3157 humpus fixed it! Thanks