I can confirm this bug. I am running Ubuntu 20.04.2 (Gnome as well) and randomly about half of the time I press "t" to open chat, not only does it open the chat context but also types a "t" in it. There doesn't appear to be any other problems, in particular I am not getting duplicate letters when I type stuff. I am using the latest Minecraft version, namely 1.18.1 (unmodded, official launcher).
I can confirm this bug. I am running Ubuntu 20.04.2 (Gnome as well) and randomly about half of the time I press "t" to open chat, not only does it open the chat context but also types a "t" in it. There doesn't appear to be any other problems, in particular I am not getting duplicate letters when I type stuff. I am using the latest Minecraft version, namely 1.18.1 (unmodded, official launcher).
Edit: confirmed for Ubuntu 21.10 as well.
Edit²: confirmed for Ubuntu 22.04.