I’ve had this issue for some time now, I’m guessing it hasn’t been discovered because no one on the dev team uses one of these super ultrawide 32:9 aspect monitors. Note that this problem doesn’t happen on a single 16:9 monitor.
When navigating from the canvas, right clicking and attempting to go into a devices setting fails. When you navigate there from the right device listing, you’re able to get into that device’s settings, but are unable to exit because the “back” arrow disappears. This behavior lasts until Signal is restarted.
I’ve created a video using nvidia’s overlay, and for some reason the video has some wacky artefacting that didn’t happen during recording - but it’s still possible to clearly see the problem I’ve outlined. I blame Wallpaper engine. Or perhaps Congress 
Hope this helps. See you on the discord.