You may try this:
toolbox create --image quay.io/toolbx-images/debian-toolbox:12
toolbox enter debian-toolbox-12
Than follow Signal instructions. You will have it installed, launch with signal-desktop
. So you enter debian toolbox and launch Signal from it, that is Fedora atomic way.
I am not telling, that is 100% better, than Flathub version, but you may try just to see if problem is still there or not. Flathub version is also built from their debian file, it should be ok, but it also may contain some issues. If I would using Signal myself I would probably use Flathub, but if I had such issues I would definitly consider trying toolbox way.
I like the way you think! Yes I agree with you, there should be some starting point for understanding privacy-washing. Yet I beleive for end user of Chrome browser this feature could be usefull and understanding what is this actually could be difficult?