Not sure about this, probably worth looking at the issues wherever these are provided from (snapcraft?) since these aren’t provided/maintained by the Fedora community. It doesn’t look like it’s a Fedora specific issue, though:
Note: I use both Signal and Discord from FlatHub (Flatpaks) and they show up fine in the application list and function perfectly. Fedora is better integrated with the Flatpak ecosystem in general. We even provide packages from the repos in Flatpak form for use on Silverblue.