You can open Discord in a private window in you browser to get another identity. On Linux, I can also recommend firejail with the --private= flag which allows you to have unlimited instances (well, limited by your RAM).
On the one hand, there are SUID binaries like Firejail and on the other, we have bubblewrap which uses unprivileged user namespaces, also used by Podman and Docker rootless containers. However, linux-hardened disables unprivileged user namespaces by default and the Arch Wiki has warnings plastered all over the Podman page about potential security risks of using unpriv user namespaces.
You speak as if these "random Arch Linux users" have written their opinions on the wiki rather than reasonable conclusions based on how unprivileged user namespaces have been a source security vulnerabilities in the past and is still seen as a security risk.
Maybe try not to let your bias get in the way?
firefox -P <profilename>
Also I have a "work" container I use for this type of thing, so that's also an option in my context menu.